In case you have Vista and a large perpendicular hard disk (over 700GB) could you please check whether you get errors from your hard disks?

This is the way to check.
Press Start type cmd.exe press enter.
Type winsat disk -flush -drive C.
You may change the letter C to the letter of the hard disk you want to check.
You should get a success response. If not please report back here and go on reading.

In case you did not get a success response, and you have large perpendicular hard disks in any form of raid with the latest Nvidia Nforce drivers installed, check for hard disk errors (nvstor or nvstor64 error) in your event viewer - custom views - Administrative events.

A parity error was detected on \Device\RaidPort1.