Have you tried using System Restore to go back to a point prior to the problem start? Probably best to use system restore in safe mode, so restart the computer and hit F8 before you get the Windows screen showing up.
To use system restore, just type restore in the Start menu search box and you should see System Restore at the top of the Start menu.
Check at the Gateway site for chipset drivers for your motherboard. This is a SATA drive, so I’m thinking you have a problem with the SATA controller.
If none of this works, you might have to do a repair installation from your Vista installation disk. If you don’t have one, you can download and burn one (using another computer!) from this site: http://neosmart.net/blog/2008/download-windows-vista-x64-recovery-disc/ This would be the last thing I’d try though.
Keep an eye on this thread though. Plenty of people around here who know more than I on drives, so I’m sure they’ll chip in some other thoughts.