This is extremely frustrating - I've logged ~128 hours on Skyrim since 25/12/12, and have suffered only the occasional CTD. Okay, not all of it was actually playing (I do alt-tab), but I'd hazard a fair 110-120 hours were actual play. Installed Dawnguard on Saturday, played for about 40 minutes in the afternoon. Came back in the evening, about 5 hours later, and now I can't go 5 minutes without a guaranteed BSOD.

Computer info:
Windows 7 64-bit
AMD Athlon II X4 Processor (4 CPUs), ~3.0GHz
4096MB RAM
DirectX 11
NVIDIA GeForce GT 240
Driver version: 8.17.12.7061

Now, Windows Event Viewer highlights a serious issue upon start-up, shutdown, and during BSOD events - that is, harddrive\dr0 has a bad block. It seems to happen all of the time now from a few months ago. Tested with SeaTools for Windows (Samsung harddrives), and one of the harddrives comes back as failing all but the SMART test (the other drive passes all - Short DST, Short Generic, Long Generic, SMART). I have run chkdsk /r on all drives to no avail (before the SeaTools diagnostic). However, I'm not entirely certain the harddrive is to blame - I tested both Stalker and Empire Total War, and they lasted longer than Skyrim now does (complete without any BSOD). I do understand not passing those tests means the harddrive has issues, but still...

The BSOD doesn't always happen in-game. It has happened on Saturday *outside* of the game (shortly after a BSOD). I had logged back in, and started surfing the internet for info on the issue - bam, it strikes. Yesterday, after a BSOD in Skyrim, it happened when I got back to the login screen - typed in password, and bam, it strikes again. BSOD on Friday when nobody was in the house, and Skyrim certainly wasn't running. BSOD on Thursday after the Creation Kit hung on closing - click for Windows to find a solution (not really, I want to close the darn thing, but it always tries to find a solution anyway), and bam. Last time before that was Christmas Day, when I'd installed Skyrim (about 5 hours after, and I recall it wasn't loaded up, everyone was downstairs watching Dr Who). The earliest dump file was the 19/12/12, in the morning (before Skyrim), and the only other dump file is from waaaay back in May 2012.

PFN_LIST_CORRUPT (0x00000004e) appears 5 times in the 11 dump files, along with MEMORY_MANAGEMENT (0x00000001a) twice, IRQL_NOT_LESS_OR_EQUAL (0x0000000a) and DRIVER_IRQL_NOT_LESS_OR_EQUAL (0x0000000d1) and BAD_POOL_HEADER ((0x000000019) each once. One error has no Bug String Check, but Parameter 1 is 0x0000010e.

The BAD POOL HEADER would have been when on the internet, so game not loaded. The IRQL_NOT_LESS_OR_EQUAL when no one was in the house. One of the PFN_LIST_CORRUPT errors was with the Creation Kit, and the final one on the login screen after another BSOD in-game. All errors point to ntoskrnl.exe as Caused By Driver, save for the one without a Bug String Check (watchdog.sys) and DRIVER_IRQL_NOT_LESS_OR_EQUAL (dxgmms1.sys). All errors list ntoskrnl.exe as the Crash Address, though.

Only 'mods' are the Unofficial Skyrim Patch, Unofficial Dawnguard Patch, Skyrim Speeds, and When Vampires Attack. All loaded in the correct order.

EDIT: Just checked, it appears the harddrive\dr0 has a bad block error started back on 22/9/12, after these...

Error - The file system structure on the disk is corrupt and unusable. Please run the chkdsk utility on the volume \Device\HarddiskVolume2.
Warning - The file system structure on volume C: has now been repaired.

This has nothing to do with the game - you have a serious hardware problem, and from the sound of it, I'd say that your hard drive is getting ready to die. If you haven't backed your data up, do so now.

That's the thing - since those BSOD events in-game and shortly post-game, everything has been fine (I haven't touched Skyrim today). I haven't tested Oblivion, too scared (despite racking up probably 400-500 hours, and only modded - and for a significant amount of time, using an unstable mod compilation that never caused a BSOD...). Stalker is rather memory intensive, and that should have caused problems. Empire should have also. Unless it's a combination of dying harddrive and disagreeing with drivers.

EDIT: Oblivion, 382 hours played (some alt-tabbed). Maybe I ought to test it just to humour myself, maybe not. Except for the last 40 hours, I'd been using a rather messed-up mod configuration (not properly merged, etc), which - while unstable to an extent - only ever caused occasional CTDs (far less since I reinstalled and redid all the mod compilations). I know the current compilation shouldn't cause any BSOD, but I'm too scared to test it...

BSODs are pretty much always caused by problems with hardware or drivers - when applications fail, they'll cause freezes or CTDs. The fact that you're getting increasing numbers of bad block errors on your hard drive tells me that the drive is failing. They don't always just quit working at once; very often they'll limp along for weeks or even months, but eventually they will die, and unless you've got a reliable backup or you're willing to spend a ton of money to have a data recovery service attempt to rescue your data from the dead drive, anything you have on the drive will be lost forever.

If I were you, I'd back up the drive and get a new one. Do a fresh install of Win 7, and then start bringing your data and other applications over.