Sometimes a reinstall of the operating system is the easiest way to tackle multiple or nonsuperficial problems with computers, since doing this will refresh the underlying operating system software and hopefully clear any corruption and configurations that may be causing the issues. Apple has progressively made the process of reinstalling easier, to the point where now it is practically seamless to pop in the Snow Leopard installation DVD and run a reinstallation, then perform an auto-update and be right back where you were, maybe. In some instances, after performing reinstallations people may find certain applications will not work anymore.
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In OS X there are times when you may have deleted items from your Applications folder that were put there by the OS X installer.
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According to reports on Apple's Support Discussions forums, an upgraded graphics card could cause kernel panics when attempting to reinstall Mac OS X Leopard from the original, included restore disk.
The standard fixes prevail again.
Why Apple says to erase your drive before reinstalling OS X 10.1 over a Security Update