|I'm assuming you have NOT been fiddling with your memory modules.|
If you get that every time you boot the computer, the hard drive is probably in the process of failing.
Check your hard drive with the manufacturer's diagnostics.
See the latter part of response 1 in this:
If you don't have a floppy drive, you can get a CD image diagnostic utility from most hard drive manufacturer's web sites, but obviously you would need to make a burned CD, preferably a CD-R for best compatibility, on another computer if you need to.
Seagate's Seatools will test any brand of hard drive.
Do the long test.
The bootable Dos versions of SeaTools can be used even if the operating system is not working properly.
If the hard drive itself tests okay, any data problems found can be fixed, one way or another.