Hi, I am having a similar problem.
I have taken out a hard drive from another computer to put in my new computer which came without a hard drive (everything else was there but).. The hard drive has xp home edition installed on it and was working just dandy on my old computer. I have been into the BIOS menu to ensure it has been recognized which it has. I then boot my computer up and the xp loading screen comes up as normal, the loading bar is moving to say it is loading, however this is as far as it goes, I left the machine on over night and it was doing the same thing this morning, still loading, nothing has frozen as the loading bar is still moving, it just wont enter the the desktop screen. No errors are coming up nothing. any help would be great. I dont really want to take it to a computer dude only to be charged a couple of hundred $'s for something that is probably so stupidly simple.