I've had a similar problem before.... but I don't know if this will help you. Using an older ATI card, when changing the monitor from a CRT to an LCD or any monitor to a different model, the XP splash screen would show, then go blank. I discovered that booting up in safe mode, uninstalling the monitor, rebooting normally and reinstalling the ATI drivers fixed it. It was very obnoxious, since I had to do this every time I changed monitors.... and she had shipped me the computer by itself for repair, so I had to guide her through this process when she got it back.
Maybe you can try something similar?