Maxtor 6E040LO 20GB-40GB desktop drives, currently exhibit a major problem under certain extreme conditions, with the fault linked to excess temperature. Symptoms such as the drive fails to be recognised in the BIOS is typical.
The results of this failure are damaging to the disk platters. The problem is not reversible, without expertise in disk technology and DiskEng would normally recommend the drive is never operated outside of manufacturer ratings. If the problem becomes apparent, avoid re-powering the drive. If problem persists after the first power cycle, then contact DiskEng as soon as possible for advice and data recovery.