[PaulGT2164]

you should do a scandisk or have a hard disk utility examine the drive, i would say the computer just had a brain fart, but i would definately back up your data

magnetic storage device as time goes on collect tiny fragments of metal and magnet stuff on the read/write heads and that can cause the disk to fail, listen for any strange loud clicking to see if thats the case

other than that i would make sure in the bios of the computer that the Prmary master is set on the actual drive and not "auto" i have seen several times where the coputer momentarily forgets it has a hard drive

also if it does it again listen and make sure that the hard drive is spinning up when it gives the error, if it is not then it could be a power problem lol