I have made a similar post, I think that they are both related to the same issue. Installing windows 7 64 bit
The issue being that, depending on what mode I set the bios in, either SATA or PATA, enables the drive to read it, which is odd, as my dvd drive is IDE, it is definitely not knackered either, it's 2 years old, been looked after and was not cheap at the time of buying either.
I bought it off ebay, it came in a sealed box, apparently purchased from Ingram micro, which I know to be a trusted source. I installed the 32 bit and it registered online fine.
I think it is installing ok now, but still, I'm concerned that PATA mode should effect and ide drive in such a way.