Hello from TOMP,
I was having similar symptoms, along with the error "windows cannot access the specified device, path, or file"
scanners would start, but go away after a few moments. Then they wouldn't ever run again. (many EXE files had this problem)
Booting in Safe Mode I was able to reset the security on EXE files back to Administrators - Full Control, to avoid getting the "cannot access the specified device...", but still it would stop during the scan, and then wouldn't run again (it got reset back to no permissions).
Eventually I found that I could REName EXE files to CMD extension and double-click Run them.
I copied the latest combofix.exe to the desktop from a flash drive.
Then I copied combofix.exe to runner.cmd, also on the desktop, and ran runner.cmd.
It ran all the way through rebooted, went thru it's stages and cleaned the rootkit that was causing the "cannot access" errors.
(note that I left combofix.exe on the desktop also, in case it was called out by it's original name on future auto-restarts during it's process, I dunno)
Then I went to C: root and reset permissions on all child objects so all the EXE files would get the permissions back so I could run them again (instead of doing each one by hand)
Then I went through MalwareBytes, SAS, etc scans, and cleaned off all the "little" viri that were still there.
Tonight I'm clean again
Edited by tomp999, 03 September 2009 - 12:54 AM.