I bought a new mobo and when I was installing the ide devices, I had a problem with the mobo detecting the cd-rom. I replaced the cd-rom with one I knew worked and it no longer had problems detecting it, but XP was hanging at the welcome screen. I tried a lot of different things, playing with BIOS, doing a clean install, changing the jumpers, etc. When I unhooked the data cable from the cd, windows would boot without hanging. I was stumped. The one thing I never tried: unhooking the power from the cd rom. I was just taking the ide cable off. I unplugged the power and booted into windows and then shut down and hooked the cd back up and it booted fine, no hang. I was blaming mup.sys because that was the last driver loaded in safe mode but that was the wrong conclusion. Anyway, I hope this helps someone else down the road. Always unplug the power to the device too.