Master/slave settings swtiched when powered off

Pardon the cross-posting. win2000 newsgroup is practically dead.

What could have happened to cause this problem? Master and slave drives were switched without me doing anything.....

The system has Windows 2000 Prof. Today I shut down powered down the system as usual - Start Shut down, etc. The an hour later powered up. When the first screen came up, I noticed the slave drive mfr/model was listed as master and vice versa. I let it start up as normal, and the desktop was like when first installed. Opened Windows Explorer and c: drive was in fact the former slave. Former master was now one of the other drive letters. All the other drives were there, but with different letters.

I also noticed something in the recycle bin - which is normally empty. It has a couple of backup folders that had been on the original master. They were 1-2 GB each, and there's no way I would have deleted those accidentally. If they were deleted it would take a minute on this machine to go thru the deletion process. So I moved them back to a safe place on a drive.

Then I hit start shutdown restart. Hit DEL and sure enough they were showing up as being switched. I set it up to manually set them back, rebooted and all came up normally again.

Now all is back to normal.