A very useful OS X troubleshooting step is to start the problem machine in Safe Mode. Restart your machine and immediately after you hear the startup tone, press and hold the Shift key.
The Shift key should be held as soon as possible after the startup tone but not before. You can relase the shift key when you see the gray Apple and the spinning gear on the display.
Remember that this is a troubleshooting step – third party software such as Suitcase won’t work nor will any Airport cards, DVD player and your modem. If the problems disappear when you Safe Boot you can be reasonably certain that that a StartupItem (such as Norton’s Antivirus) is causing the problem.
[Here's](http://docs.info.apple.com/article.html?artnum=107392) what Safe Booting actually does:
- It forces a directory check of the startup volume.
- It loads only required kernel extensions (some of the items in /System/Library/Extensions).
- Mac OS X 10.4 Tiger only: It disables all startup items and any Login Items.
- In Mac OS X 10.3.9 or earlier, it runs only Apple-installed startup items (some of the items in /Library/StartupItems and /System/Library/StartupItems – and different than login items).
- Mac OS X 10.4 Tiger only: It disables all fonts other than those in /System/Library/Fonts .
- Mac OS X 10.4 Tiger only: It moves to the Trash all font caches normally stored in /Library/Caches/com.apple.ATS/(uid)/ , where (uid) is a user ID number such as 501.
Taken together, these changes can work around issues caused by software or directory damage on the startup volume.