I have two PC's on a network, and each has a second SATA hard drive named F: for backups.  These drives are normally not spinning except when they are written to in the middle of the night.  About a month ago, I noticed that my F: drive was no longer in the Explorer tree, no longer listed in the device manager, and listed as a disconnected network drive on the second PC.  Since I had no idea why this would be, I did something random: turned off the PC, opened it up, vacuumed out the dust bunnies, and plugged and unplugged the connectors at both end of the cable between the motherboard and the drive.  It reappeared after I booted up again, but not for long, of course.  I have done this a few times now.  Rebooting alone does not necessarily restore the drive.  Lately it has been stable, but I don't trust it.  Does it sound like the drive itself is failing, or is there something more horrible going on that won't be cured by replacing it?  One clue: the drive itself is quite warm to the touch.  The main exhaust fan of the PC is gently blowing warm air out the back of the case; I presume that, if it were a fan problem, the microprocessor would overheat and cause a shutdown before the drive would fail.
Details: the PC is a Dell Dimension 4700 series, about 5 years old, running XP.  The troubled drive is 80GB SATA, 5400 RPM (if I remember right - it's from 2005).