System cannot find hard disk

I have a Dell Inspiron 1525 (2 yrs old) with Vista Home Premium, 32bit, Intel Core 2 Duo Processor, 4GB RAM, and 280 GB hard disk with 70% free space. On several occasions, recently, my system stopped responding. I don't get a blue screen, but I do get a message indicating that the hard disk cannot be found. Each time I run checkdisk, the only message that might be of concern is "49 reparse records processed. The other messages are: "0 unindexed files processed", and "usn journal verification comple". Once I restart my system, it boots up just fine and runs okay - until the next episode.

What could be causing my system to lose communication with my hard disk?
Thanx in advance for your thoughts.

I would do a system file check and a malwarebytes scan.

http://www.vistax64.com/tutorials/66978-system-files-sfc-command.html

Tutorial:Thanks to Brink

Malwarebytes

EDIT:Schedule a disc check for next start up as well.

Hello

Here is how to do the check disk...

http://www.vistax64.com/tutorials/67612-check-disk-chkdsk.html

Check Disk (chkdsk) - Read Event Viewer Log - Windows 7 Forums

If the above test prove negative, go one step further while testing your hard drive

Test Hard Drive HD Diagnostic or this test Hard Drive Diagnostics Tools and Utilities (Storage) - TACKtech Corp.

Hard Drive Testing Tools - Top 7 Free Hard Drive Testing Tools - Hard Drive Diagnostics

If the ckdsk, suggested in the above post, is positive, you have your answer.