Hardware explanation

Ok, so WinXP had a huge fit when I installed the newest video driver update. Total crash, and i had to reinstall. So I was trying to install winxp again, but it kept sayin i had a bad cd. I i thought, ok ill install linux. that didnt work either. So after many CMOS clears and a ton of other stuff, I unplugged all power and set the box aside. Just to get a better look inside for any obvious problems, like gnomes with hammers, i unplugged the HD. Now remember, the power was off, no power supply plugged in! Just to clarify, i did clear the CMOS with the power unplugged. So today, I tried again. It worked perfectly, and i think it was because i plugged the HD in and out? is that it? I dont understand how anything could have changed when the power was off. can someone please link or let me, or let me know how stupid i am?

It's black magic. I have had wierd things like that happen to me. Just be thankful, you don't need an explaination.