Here's a real mystery. The system is XP Professional updated with all available updates with 4 GB of RAM. When booting normally, it is slow. Very slow. V E R Y slow. Like over an hour to get to the desktop (possibly longer - I just couldn't sit in front of it that long timing it). Then once it's booted, it's still slow. Things that should happen instantly, like bringing up the Start menu take several seconds. Things that should take a second like opening the Control Panel take nearly a minute. While I'm waiting for things to happen, the disk activity light is pegged on solid.
But the really weird part is that it boots quickly and normally into Safe Mode. Before you think you know the answer, read on.
Here's what I've tried so far. None of these has helped.
Ran AVG in Safe Mode - nothing found.
Ran Malwarebytes in Safe Mode- nothing found.
Rolled back the system two weeks - didn't help.
Did a chkdsk /f - nothing found.
Defragmented even though it said it wasn't needed - no change.
Ran theSeaTools for DOS disk diagnostic (it has a Seagate drive). Passed both the short and long tests.
Used msconfig to enable a diagnostic startup (removes all optional startup items). Still takes forever to boot normally.
No new hardware has been added recently.
No new software has been added recently.
The only two clues I can find are
1. Constant disk activity
2. A system log full of hundreds of Error 7001 "Service Control Manager" messages.
I'm stumped. Any ideas would be greatly appreciated.