My sons computer came up with a NTLDR error, because he had a relativily small harddrive I decided to install another one. Brought his computer in to the office, power supply was dead, replaced powersupply, point that I am at now
If I keep the "bad" harddrive in it shows the NTLDR error
If I make the CD rom primary boot and put the xp c in it will try to install it
If i take another hd out of a working computer it will not boot at all,
i get a disk read error, ctrl alt dlt to reboot

I have already:
checked cmos and it is reading the hd as the primary, changed cables 2x, I KNOW it is a good harddrive because it will boot the computer i took it out of

also began getting the onboad realtek lan error but disabled that in cmos

am looking for pointers as to what to do next!!!
help for sanities sake.