I'm running windows XP and have three physical hard drives. The first is partioned into C: D: and E:. The second was added later and is F:, and the third added even later and is G:.

Ever since the G: drive was added, I periodically "lose" the F: drive, even though bios sees it. Then after a reboot or two it comes back. (Needless to say I've backed it up, so don't tell me to do that). What could be going on and what should I do?

One thought is that the F: drive is too full--it is 250 gb, with a little more than 5 percent free, but I don't see how that could cause this sort of problem.

Hi,
Please try the followings:
1.Delete some of your less important folders or programs.
2.Run detailed scan check looking for bad sectors and if necessary format ,then paritition your disc.
3.If fault still there,then down load a hard drive diagnostic tool from the disc manufacturers website,it is usually Free.
I hope the above will solve the problem.Let me know if you need any help.