Today I spent some time helping out a colleague who was experincing strange behavior with her computer. And then I had to do many of the same things on my computer because it was acting wierd. These steps apply to both Windows and Mac OS X. Most of the things I do are simple steps even someone with the most basic computer experience can perform. I developed many of these steps in my 12 years of doing corporate IT, none of them are magic, they work and often take care of most issues.
When your computer is not behaving try these simple steps:
1. Shutdown your computer, wait 5-10 seconds, and restart it. Sometimes computers just need a refresh.
2. Check for updates. When you perform step one you may notice your computer installs updates. When your computer is turned on again go look for updates. Sometimes computers start acting wierd when updates are waiting to be installed or have installed and the computer has not been rebooted (even when the update does not require a reboot). 
3. Keep running the updater until it says "No updates are available" and reboot one more time. Sometimes programs like Java also have updates waiting and can cause issues with the way a computer performes; check those updater programs too.
I can't tell you how many times the most strange behavior was corrected by doing step 1. Printing problems, network issues, display problems, programs crashing, etc. I know it can be a pain, but sometimes you computer needs a micro cat nap to regain it's senses.
Please don't use the comments to flame one side or the other. This is not the place for such discussions. I've spent time doing high level tech support for both platforms (and currently have both Apple and Microsoft products in my home). It really doesn't matter what platform, I'm ambidexerous and can make either sing, and both have their issues from time to time.
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