I have a customer's laptop in which is worrying me. This is the second time since mid-December that I've seen this laptop, and both for the same reason (though I cannot remember the exact circumstances of what happened last time) - on both occasions, the reason that the customer wanted me to look at the laptop for was that Vista wouldn't boot. I believe a disk check fixed the problem last time, but I can't remember with certainty (though since typing most of this post I think I had to get bcdedit to properly write the boot configuration information again). I certainly would have run a full disk check on that occasion, and I very much doubt I would have concluded the work before running one. I think I'll try to dig out the event log entry to check the results now.
Anyway, on this most recent occasion it was the classic 0x00000024 (UNMOUNTABLE_BOOT_VOLUME) BSOD. The recovery console wouldn't work so I booted from my Vista OS DVD and ran a full disk check from there. The full disk check didn't find anything particularly interesting (like say bad sectors/clusters), and the laptop still wouldn't boot normally but would via recovery console from the hard disk, at which point Vista's automatic repair fixed whatever issue extremely quickly and automatically restarted/booted successfully.
So, the machine boots. No particular problems to speak of, it goes on the Internet fine, Malwarebytes (fully updated) picked up a few bits but nothing that suggested anything was actively screwing up the machine (things like data files for MyWebSearch but no binaries or registry entries to suggest anything could be auto-starting, no CLSIDs, etc). The only niggle initially was that UAC would regard every executable as unsigned, but then a Windows Update fixed that. A few days later however (not the next boot or anything like that), that UAC problem happened again and was fixed after a Windows Update. I had the network cable disconnected before that second UAC problem happened, but I can't believe that Windows is normally that touchy about it.
I also want to run a full disk check on reboot, except Windows just restarts normally with no console-type messages and nothing in the event log. I tried a few suggestions on the Internet for SessionManager edits, but it made no difference. Also, the machine won't boot into the recovery console from the hard disk.
Summarised, my feeling is that there's something not right with this machine, possibly malware, but I can't put my finger on it. Google searches for security sites are working fine, and apart from the chkdsk and recovery console issues, I can't find anything else currently wrong. I could try a full virus scan I suppose, but I don't have a great deal of faith in that finding anything interesting.