Jibu

hey, I'm having an unusual problem with my computer. When the computer is booting up, it passes the "Compaq" logo and the Windows XP splash screen fine, but when the screen is supposed to go blank briefly after the splash screen, 2/3s of the time the computer doesn't pass that point.

This has only started happening since yesterday. It occurred right after I had installed a new modem into the system. I had also switched around some PCI cards to try and fix a freezing problem I was having before. I'm not sure if this is related to the problem, but I know it has been happening since I installed the modem. I tried removing all of the PCI cards (including the modem) except for the graphics card, but the problem persists. Also, I checked the hard drive LED when the screen changed from the xp splash to the blank screen (just before it is supposed to go onto the log on screen) and the LED basically stops by the time it gets to that blank screen--it may flicker every few seconds or so but that's it. When the computer boots up normally, though, the LED flickers throughout the boot. At least every other boot has been giving me this problem. I end up having to manually shut down the system and reboot again when it happens.

PLEASE help
thanks