Thanks for the reply.
I don't think it is a hardware problem because the HDD i'm going to install Windows 7 on is functioning, since I can see it in My computer (I have two hard drives, one with XP and one that i formatted for Windows 7). I can't check the MD5 though becuase I deleted the original ISO. Could a source of the problem be a scratched DVD? Because mine has a few scratches on it which could be the case. I'm going to try downloading another copy and then burning it to another DVD. (with no scratches