I'm no computer savvy but somehow it feels good whenever I can extend help to people who are having computer issues like the common slow speed and poor performance. Aside from removing temporary files and defragmenting the hard drive on a regular basis, I also recommend the use of special software like Windows 7 Registry Cleaner to keep the registry healthy.
In layman's term, if the CPU is the main brain of a computer, the windows registry serves as its central nervous system where the configuration settings are stored and in less time can be highly susceptible to security vulnerabilities if not guarded safely. Why do you think you suddenly get those annoying error messages and/or experience aimless crashes? I also asked the same questions before... now I have them all answered. Thanks to JK, my ever supportive mentor. He has always been there to help make things easy for me all the time.