In the past I've used Norton utilities for defraging among other things, but apparantly they are not updating for newer os x's. So I purchased Drive genious by prosoft. Otherwise there are a few things to consider. Firstly, though, that there is some disagreement among mac experts as to the neccessity of doing certain things. And ideally, you should back up important data before trying anything. I would say repair disk permissions and shut off any background programs. And then use this list of suggestions before buying any new software. Good luck, Brian General Steps in OS X Troubleshooting These are not listed in any particular order, nor do all of these steps apply to all cases. Different problems require different solutions. Software Log Out/Log In. Sometimes a quick log out/log in will fix a simple problem. Restart computer. See above. Zap the PRAM. Reboot your computer while holding down the command-option-p-r keys simultaneously. Don't let up until you have heard the startup chime three or four times. If you need assistance finding the command key on your keyboard, see image at bottom of this post. Reset Open Firmware. This is a step for G3, G4, and G5 Macs only. If you have an Intel Mac, you should Zap the PRAM (see previous point). Reboot your computer while holding down the command-option-o-f keys simultaneously. At the prompt, type reset-nvram and hit the Return key, then type reset-all and hit the Return key again. Your computer will reboot. * Note that these commands are correct for New World machines, those with colored plastics (iMacs, Blue and White PowerMac G3) and newer. Old World machines (G3/233 All-in-one, beige G3, etc.) are slightly different--just type the reset-all command. Repair Permissions. Open Disk Utility (by default, it is located in /Applications/Utilities). Select your boot partition, then click the First Aid tab. Click the "Repair Disk Permissions" button. File System Check. This can be done in several ways, including 1. Boot to single user mode by holding down command-s during the boot process, then at the prompt typing fsck -y and hitting the Return key. Continue to run fsck -y until no errors are found. (Note: if your hard drive is journalled, you will need to run fsck -yf. Attempting to run fsck -y will result in a message reminding you of this. Thanks to Petroffski.) Then type shutdown -r now and hit the Return key to reboot. 2. Boot to a full OS X Install CD. From the Installer menu, select Disk Utility. Select your hard drive boot partition whose file system you wish to check, click on the First Aid tab, and click the "Repair Disk" button. 3. Boot to a third party disk utility CD and run the file system check offered therein. At this time, I can recommend DiskWarrior http://alsoft.com and Drive 10 or Tech Tool Pro 4 http://micromat.com . The third party disk utilities generally do a better and more complete job than the first two options and have been known to rescue drives that are inaccessible. Reset PMU. Software PMU reset is ONLY for Apple portables, not desktop computers. The procedure is specific to each machine, so I can't give a synopsis here. Instead, check Apple's Knowledgebase article for resetting PMU on iBooks and PowerBooks and Apple's Knowledgebase article for resetting PMU on MacBooks and MacBook Pros. This does roughly the same thing that pressing the PMU button or CUDA switch does for desktop Macs (see the Hardware section below for more information). Log in to clean user account (or create a new user account if necessary). Many problems are user-specific, and knowing whether or not this is true about a specific problem is an invaluable piece of troubleshooting information. If a problem is found to be user-specific, then it can often be traced to a corrupted preference (.plist) file or corrupted caches. Trash the prefs. If a problem is related to a specific program, try trashing or renaming the preferences file associated with that program. Preferences that are unique to a single user are found in /Users/shortusername/Library/Preferences/ (where shortusername is the short username of the user in question.) Preferences that are common for all users on the computer are found in /Library/Preferences/ So for example, if iTunes crashes, try renaming Users/shortusername/Library/Preferences/com.apple.iTunes.plist to /Users/shortusername/Library/Preferences/com.apple.iTunes.plist.old while iTunes is not running. Re-launch and see if the problem has disappeared. Disable hacks. Yes, Mac users tend to love our system enhancements, and there's nothing wrong with that. But when we run into problems, they are always suspect. When troubleshooting, always disable system hacks. Disable Startup Items. In the same vein, there's nothing wrong with Startup Items, but when troubleshooting problems, an important step is to disable programs that automatically start up. In OS X 10.2, they are found in System Preferences > Login Items, or you can look in the Terminal at /Library/StartupItems. The similarly-named /System/Library/StartupItems should be left alone. Install the combo updater of your OS. In some cases, computers which were updated to the latest point release of OS X using Software Update have had problems which were fixed by downloading the combo version of the same release and installing it overtop of their existing OS. For example, if someone is having problems with OS X 10.3.3, they may wish to download the combo version of 10.3.3. Update your firmware. Although Apple does not tend to release frequent updates for firmware, in some cases (like the early CRT iMacs) it is vital that people update their computer's firmware before updating their OS. In other cases, an older version of the firmware can cause flaky behavior. In any case, check Apple's support pages for firmware updates for your computer. Clear system and user caches. One way to do this easily is with Cache Out X(thanks to john wilson), or with Jaguar Cache Cleaner / Panther Cache Cleaner/Tiger Cache Cleaner or else here is a more DIY method. Uninstall Recent Software Additions. If installed something directly before the problem began, even if it appears unrelated you should uninstall that software package as a troubleshooting step. Check what your Console says. If your problem has a specific event associated with it, for example an application quitting unexpectedly, then open up the application named Console (it is in /Applications/Utilities) before the event. Trigger the event and see what messages simultaneously appear in your Console. Safeboot. Reboot and just after you hear the startup chime, but not before, hold down the shift key. The procedure is explained more completely here: http://forums.osxfaq.com/viewtopic.php?t=4680 . In some ways, this step is redundant with the Disable Startup Items and the File System Check (1. fsck) steps above, but since it does not involve the terminal or any changes to your setup, it may be preferable for some people. Reinstall System. This should be a rare step, but in some cases it is best to reinstall the operating system. Hardware Check for hard drive space. Your computer must have adequate hard drive space to operate normally. Check to make sure that your hard drive has at least 5% if not 10% of it's capacity available for use. If it doesn't, then buy a bigger hard drive or delete some old junk immediately. Verify hard drive age. Hard drives do wear out over time. If your hard drive is around three years old or older, you should be much more diligent than usual with backing up and it may be time to think about replacing it. If you are having continuing problems with disk corruption, bad blocks, or other drive-related issues with an older drive, these are warning signs--you should definitely replace it immediately. (Thanks to Mark Hollis.) Memory checks. Run a thorough memory checker overnight. If you are comfortable with the command line, I'd recommend memtester Download / Information or if you prefer a GUI, try Rember. Run Apple Hardware Diagnostic CD. If you have one, it can be useful in some cases. Remove Unnecessary Peripherals. Other than keyboard and mouse, remove all peripherals attached to the computer, including any hubs. Remove Unnecessary cards & memory. Other than one main Apple-provided video card, remove additional expansion cards. Although making your computer have less memory is usually a bad idea, if you can't explain a problem any other way and don't have a good memory checker available (or can't get one to run because of problems), then you should remove additional memory other than the original Apple-provided memory stick. Push the hardware PMU (or on older computers, the CUDA) reset button. Most desktop Macintoshes have a small button on the motherboard called the PMU or CUDA button, often near the PRAM battery. If you are having serious problems, you may wish to turn off the computer, hold the PMU button in briefly, wait for 10-15 seconds, then turn the computer back on. Don't press the PMU button twice within 10-15 seconds: Apple claims that this can have negative consequences. Replace PRAM battery. Many Macs have a small battery on the motherboard which powers the PRAM when the computer is switched off. When the PRAM battery is low or depleted, some odd issues can occur. The simple fix is to replace the battery.