XP PC will hibernate but not standby
XP SP3 Media Center Edition 2005
4x SATA HDDs
1x eSATA HDD
Since reformat of the HDD that holds the O/S and application software the computer will not standby; a split second after selecting standby the screen goes black and the power LED on the front panel starts flashing (correct, for standby), but all the disks continue to run and at least one of the cooling fans spins up to max speed the same as it does in the seconds between power-on and POST success.
Interestingly, it will hibernate, and resume from hibernate, perfectly. Only standby has the problem. Before the software reinstallation described above it would both hibernate and standby, perfectly.
The problem does not appear to be USB related and none of the troubleshooting information I have found on the web fits my problem description. I removed all power including the BIOS battery for an hour, but this made no difference. Likewise unplugging the eSATA HDD before power-up, powering up, and then trying to standby; no difference.
Other suggestions, please?
The PC is scrupulously well house-kept and is completely up to date with Windows Updates.
TVM,
XV