1. SAFE MODE
Read http://www.google.com/search?&q=XP+SAFE+MODE if you don't know how. This is a simple test to see if there is a hardware issue. Safe mode, if it works can point to an OS issue.
2. SYSTEM RESTORE to a day it worked fine.
Use http://www.google.com/search?&q=XP+SYSTEM+RESTORE if you need help with this tool.
This post is for a friend of mine who has an HP 503W with 128 meg of ram. Recently after her son installed a game called "Hello Kitty", she started having problems with her pc. Figuring it was the game they had installed, she uninstalled it. However, it did not do a complete uninstall, so she just did a system restore through Windows XP. Now, her computer will boot up as far as the icons appearing on the desktop and then it tries to access the CD drive and then the screen just goes black. She has to turn it off and back on and then it is the same thing all over again. What could be the cause of her trouble? What could I do to check for what could be causing her problem? She swears she is gonna take a sledge hammer to it......lol!