Monitor stop working after memory and usb 2.0 upgrade

Hello,
Thanks, After I installed a usb 2.0 card and triple my memory size. my monitor after about an hour stop working. I tried everything (or almost everything that I know). I reseat the battery on the motherboarb, disconnect and reconnect almost every wire, use different monitors` that I know works, still their is no signal going to my monitor when I boot.Your help is greatly appreciated,thanks. specs: windows xp home edition