Problem is HDD? Help please.

I built this system 3 months ago with no problems until a few days ago...

Gigabyte EP35-DS3L
Intel E8400
2 x 2gb 6400
ATI 4850
LITE-ON DVD
OCZ 600W
Seagate Barracuda 500gb 7200rpm 3.0gb
Vista 64

I boot it up a few days ago, and it wouldn't go past the initial splash screen (hit <tab> for post, <del> for bios, etc..). I could go to post, but couldn't even get into BIOS much less boot.

So I popped the case open. Initially I tried to swap different memory sticks, but still couldn't get past that splash screen... so I removed the CMOS battery for a few minutes and tried again. Now I can get into BIOS just fine, but the system still won't boot. The hard drive doesn't appear to be recognized in BIOS, and if I try to start the system normally it tells me to insert the CD to boot with. I made sure the SATA cables were all attached correctly and double checked that the boot priority is HDD first.

So I put the vista OS in to make sure that worked properly and it went through, but the hard drive is still not appearing for me to install windows (obviously). Tomorrow I'm going to pickup a new HDD and try that out.

My questions are: would a bad HDD stop BIOS from loading? Am I doing something else wrong?

I'm still new at this. Any help would be appreciated.