I have just reinstalled XP Pro on a machine that had XP Home on it. I did this because all of a sudden - I couldn't get my sound card to work, - couldn't get the onboard sound to work, - the USB mouse quit working and - the system couldn't find the boot record when booting. I've tried 3 different mice (which all work on other machines) and the only one that I could get to work is my laptops USB wireless. Go figure. I'm still having boot problems, and still can't get the sound to work. I've read other threads where some hardware symptoms, other than obvious CMOS errors were attributed to worn out lithium battery. I don't think I've ever replaced this battery. Could this be the problem?