Windows 7: nvstor64 error type 3 is causing my PC to hang repeatedly

Bottom line up front - my PC is having repeated nvstor64 type 3 errors which cause it to hang and the only way to restart it is to hold the power button in until it shuts down. Help!

Full details here:
Early July my PC started acting odd. Freezing, running slowly etc.
- I ran a virus scan from windows - nothing
- I ran another virus scan from a Linux CD which found a couple of things but nothing terrible and, after cleaning, the PC was no better.

Chkdsk revealed some lost clusters. I repaired those and ran sfc /scannow to repair the OS, which it did.
A day or so later, still acting odd, I ran another chkdsk and...more lost clusters. A disk check utility in Ubuntu reported that the drive was failing so I bought a new drive, cloned the old drive onto it (it was still working) and...nothing!

• I read a thread that said it could be the sata cable, which didn't make much sense but I replaced it anyway and...still nothing!
  
• Another thread suggested updating the disk drivers. When I try to do that it tells me I already have the latest driver installed. Should I uninstall and reinstall anyway?
  
• Finally another thread said to update the bios...but I have no idea how to do that or whether it's worth the effort.

the nvstor64 errors started on July 4th, about a week before I messed with anything. No idea why they would just start appearing like that but I am still getting the nvstor64 errors about every few minutes and I'm about ready to put a sledgehammer through it.

Please help!

PC is an Acer running Window 7 64 Home Premium, 4gb Ram, Barracuda 1TB drive

OK...I figured out how to upgrade the bios but the problem is still there.

heeeeelp!