It's running XP Pro, everything seems to be connected fine. Recently I'd opened the case up to remove an old CD-RW drive that was malfunctioning, but I fixed the drive and returned it back to its original spot, and it worked fine. But today when I turn on the power, it shows me the Asus motherboard boot screen, then the XP Pro loading screen, which appears with the moving 'loading' bar for a good three to five minutes, at which point it goes back to the motherboard screen. I've tried removing the drive, and turning the power supply off/on then attempting to reboot. Still, it won't move forward past the Windows XP screen, at which point it goes back to the motherboard screen. What could be the problem?