Get the product code and submit it to Microsoft to verify whether it is a legal copy.
More information at http://www.microsoft.com/piracy/YourPC.mspx

Have you tried playing them with VLC? http://www.videolan.org

It could be viruses. Try scanning your computer with anti-virus program.

EasyCleaner will do for you.
http://personal.inet.fi/business/toniarts/ecleane.htm

I think it's your monitor problem. Not your OS.

Use alternative software like openoffice. http://www.openoffice.org it can be used like M$ office. One good thing is totally free. :D Hope it helps

Try removing them using EasyCleaner. I am currently using it too.
http://personal.inet.fi/business/toniarts/ecleane.htm

WMP cant play avi. You can try http://www.divx.com

Try

Control Panel -> System -> Advanced Tab -> Startup and Recovery setting -> Disable Automatically restart

Hope it works.