Do you have access to another machine? Can you create a bootable CD/DVD and run this?: RAM - Test with Memtest86+
If you can't do that, check your machine's BIOS to see if there's a memory testing facility there.
If the memory checks out okay you can see if there is a quick hard drive test available in the BIOS. I wouldn't run a long test just yet since you have data there that you need; I'd get a copy of the data first if you suspect the drive might have problems.
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