1). You have changed a registry key that changed a command for the HD to spin down to conserve energy, or (in a strange case) spin down to prevent data corruption.
2). The excessive heat has fried the data chipset on the HD that relays directives from your CPU to the velocity engine to speed up (data read) or slow down (data write) Most likely *if this is the problem* the CPUs message of READ is tranferred and corrupted, so the HD is doing its default execuation of unknown data, in otherwords, its velocity is being set to WRITE mode.
Solution to #1, check all BIOS settings for startup and Windows settings for drives.
Solution to #2, A new HD is the only real solution for this problem, but you may want to check to make sure this is the problem first by closely monitoring you total free space on the HD (monitor it very closely!!!) If you see it change everytime that happens by even 500bytes, then Problem #2 may be the problem.
Sorry about your bad luck Other.
GL fixing it.