i am getting a message after the boot process that says: "Windows failed to start, a software or hardware change may be the cause, please insert the installation disc and press enter", i did just that and i am still stuck here, i also ran a test for the memory and the memory seems to be O.K, should i clear the RTC CMOS, my computer specs are: P5KC MOBO, 4GB Ram Memory, 1 TB 300 Sata 32 MB, Intel Quad Q 6600, 8800 GEForce VideoCard, Windos Vista Home Premium. Please Help, do you think my hard drive is damaged?

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.
Good luck.

Does the drive show up in the BIOS? If so, download the drive tools from the manufacturer and test it. If it's good then reload Windows.

google the ultimate boot cd. Run memtest for a while - this will see if you have any data corruption issues in the system. If you do- its going to tell you, and thats why your hard drive did that. Ultimate boot cd has hard drive testing tools as well, i'd start there.

the hard drive is not detected in the bios, i also tested it in another computer and it wasn't detected as well, that means that it is damaged?

If the HD is not detected in two different machines then it probably is dead.

if this is a sata drive, and its not detecting in any port on the motherboard with any cable in the bios, its dead.

Yeah, especially if it is not detected on two completely different machines.

Buy a new HD. Of course, that assumes that you have changed cables.

If it is dead in the BIOS of two machines, then it is dead. No other posts beyond this will change the truth.

Throw it in the trash and get a new one.

Sounds like it is dead for sure. But if you do have a spair cable around try it out.(Assuming you used to the same cables in the other machine). In a past machine i had set up, one day one of my drives stopped showing up in windows/lunix/bios. I took it out and put it in a external case and it worked fine. Put back in the machine didnt work. Turned out somehow that the ide ribbon cable got fuxored up somehow. Just didnt work anymore. I didnt open the case and move anything around prior to this either. Put in the drive with a different cable and fired right up.

So the drive is probally dead, but do check it with a spare sata cable/power cable just to 100 percent sure instead of 99 percent. The chances of a sata cable failing is probally even less the ide ribbon cables.