After upgrading my memory to 512mb I keep having my monitor freeze up. I've checked all connections and they seem ok. The computer is working GREAT due to the fact that I was burning a DVD and the processing light kept blinking and when the burning program was done, I could hear the notifier telling me it was done. Any clues out there what may be the problem???  I have tried 4 different sets of ram.Test the RAM.
http://www.memtest.org/
http://oca.microsoft.com/en/windiag.aspDoes the computer have these problems while running in safe mode. Its not forced to be your RAM try this. Update antivirus and run a scan. Run a program called SPYBOT search and destroy its a free download. CHECK to see that the computer isnt overheating. take side cover of while the computer is switched off and vacume out any dust you see use the plastic end of the vacume. Run a thorough scan disk of your hard drive and lastly if still no joy go here and run the trial version of this. http://healthycomputerclub.com/Software/PCRescue/index.html.Have you disturbed the graphics card......while messing around in the case?.......reseat the vid card.....and check you have the correct drivers for it.........boot to safe mode......hold down the f8 on boot........and run this test....type dxdiag in the run BOX.