Well, re-installing windows isn't necessarily the first thing you can do. Does it ever give you a blue screen? Things like spyware programs or viruses can do such things if you've got one.
And as for the HD, do you use a normal HD or a SATA HD? If you use a SATA drive you'll probably need the disk with drivers to install at the loading screen when the Windows CD first starts up (and asks you if there are any drivers you wish to install). Otherwise, it won't recognize you have a SATA and say you have no HDs installed. If you have a normal IDE HD and its doing that, then that's a different matter.
I guess to really help, more information on the problem would be useful. Bluescreens usually contain error messages (if you're getting them) or anything you might do that causes the freeze would also be useful.