Clearing the RTC probably wont help. It would be better to go into standard bios, and have it auto install your drive.
There are a number of reasons why your hdd is not working. The first thing to do is make sure all cables are properly plugged in at all ends. Then go into bios, have it autodetect the drive, then turn on disk check.
Even if your bios does not see the drive, it does not mean it's dead. It could be you have a bad cable, or psu.
Once you are sure the drive is okay, you cant just blame vista. It could be that someone has deleted a key file, amybe even remotely, or you may have a virus.