How do i fix my pc? any techies out there?

ok so i have fujitsu siemens scaleo p desktop, it`s about 2 years old. Bought it brand new never changed any hardware, recently it froze up and now doesn't recognise my 250 gb sata hard disk. I thought it may have been the hard disk that failed so i swapped for an old 80 gb ide hard disk which is recognised by the bios. My problem is when i do a fresh install of xp i just keep getting looped after the first restart of installation. I have reset the cmos battery also but no joy what can i do? i know it is not a hard disk problem at least not on my old 80 gb hd. Can anyone help? Many Thanks!