Hm. Not sure I really want to share this, but...
My current computer, running an AMD 5-something and WinXP Pro, was making noises. Scary noises. Hard Drive About To Die noises. Oh, and I was getting Blue Screens of Death every several minutes.
I opened the case and by holding my hand on the hard drive, confirmed it was making the noises because I could feel the noises.
First thing I did was run a full backup. Since I do this weekly, it was quick, and the files verified OK. Whew!
Next, off to the store, got a new 1 TB drive, copied the old one to the new (Norton Ghost is getting long in the tooth, but still valuable).
Removed the old, rebooted...and the noise is
still there.
...Turns out the 3.5" floppy had died, NOT the HDD. sigh. $80 wasted. (Not completely: I still have a perfectly good 1 TB HDD for my next machine.). BSOD was because the FDD was telling it weird things. Go figure.
The lesson:
Just because you found the symptom you expected does not mean it is caused as you expected.