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I have this home-built computer running Windows Vista Ultimate x64 for a couple years. The OS is not pirated, and the hardware is pretty boring: 8GB of RAM, Intel DG45ID motherboard, Core 2 Quad processor, no PCI cards, two hard drives, no optical drives. Simple stuff.

It was working great until the last few weeks, when I got two or three bluescreens that I couldn't explain (and which may or may not be related). Then last night I woke the computer up from sleep (as usual), and it got to the logon (fast user switching) screen, then bluescreened. Upon rebooting, it bluescreened again just before the logon screen, and has done similar ever since.

Sometimes I get a "{fatal_system_error}" BSOD, and sometimes it just reboots while the screen is still black, before the circular Windows logo appears in the middle of the screen before logon. But it's always one or the other: I haven't seen the logon screen appear even for a moment since the first resume from sleep. There seems to be a bit of extra hard drive thrashing before the reboot--maybe it's writing the crash dump?

I've seen stop codes 0xc0000021 and 0x00000001. From my reading it seems that Microsoft says the problem could be a misbehaving service, so I went into safe mode (which works!), and used msconfig to disable all services and startup items I could. Still the same. I ran the boot-time memory checker, and it was fine (plus, the computer works in safe mode).

The most recent changes to the computer were to update the audio & video drivers (from Intel's site), and install Nero MediaHome 4 (DLNA server, came with TV). In safe mode I've uninstalled all of these.

I used to have a PCI Wi-fi card (which I wasn't really using), so I took that out, plus I unplugged my secondary hard drive, all to no effect.

I ran MalwareBytes' Anti-Malware, and it found two things: a "fake alert" trojan and a "password gen" one. I imagine these are both from browsing the web; I removed them both and now it reports no problems. So I guess this all could be the result of a virus, but it seems strange--what virus would want to make your computer simply stop working?

I'm having a hard time figuring out what to do next. Your suggestions would be much appreciated. Please don't bother suggesting that I reinstall Windows; I know I could do that, but would really prefer not to (because it will take quite a while to get everything set up well again).

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Run sfc /scannow in safe mode, and also do a chkdsk /f to ensure the system files and file system are both intact. – user3463 Jan 21 '11 at 3:22
I radid, but it didn't help (said everything was fine). Thanks for the idea anyway--I didn't know about sfc. – John Zwinck Jan 22 '11 at 19:04
up vote 0 down vote accepted

After trying desperately to remove recently-installed software and disabling all services, all to no effect, I thought to try the boot option "Last known good configuration."

It worked! I still have no idea what caused the problem (possibly Nero MediaHome?), or even precisely what the problem was (the BSOD was vague). But last-known-good actually solved the problem...I think I hesitated to try it earlier because my experience with it years ago was that it never seemed to help (on other computers, back in the Win2K/XP days).

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