BSOD twice in 5 days (ntoskrnl.exe/ntkrnlmp.exe and ntfs.sys)

Quick update:
Chkdsk yielded no result, although the test for drive C: (the Windows installation, which I had to schedule for the next restart) didn't seem to do anything. All it said after detecting the drive and file system was something along the lines of "Drive is clean".

I went for Seatools afterwards, which did find something in drive F: the external 1.5TB Seagate FreeAgent I've got.

08/07/2012 03:55:27
Unit Serial: 2GEX6TKT
Unit Model: Seagate FreeAgent
Model: ST31500341AS
Serial Number: 9VS1DRE9
Firmware Revision: CC3H
Short DST - Started 08/07/2012 03:55:27
Short DST - Pass 08/07/2012 03:56:32
Identify - Started 08/07/2012 03:59:45
Short Generic - Started 08/07/2012 03:59:59
Short Generic - FAIL 08/07/2012 04:00:03
SeaTools Test Code: A6D2D9C4
Short Generic - Started 08/07/2012 04:01:56
Short Generic - FAIL 08/07/2012 04:02:00
SeaTools Test Code: A6D2D9C4
Long Generic - Started 08/07/2012 04:02:47
Bad LBA: 120 Not Repaired
Bad LBA: 228628921 Not Repaired
Bad LBA: 228629042 Not Repaired
Long Generic - FAIL 08/07/2012 08:21:29
SeaTools Test Code: A6D2D9D4
Long Generic - Started 08/07/2012 13:18:23
Bad LBA: 0 Not Repaired
Bad LBA: 121 Not Repaired
Long Generic - FAIL 08/07/2012 17:25:29
SeaTools Test Code: A6D2D9D4

Could the external drive be the reason for the problems? I'd disconnect it just to make sure, but seeing as sometimes I can go 10 days without a BSOD, I'm not sure how reliable that would be.

edit: Also, here are the reports of 2 new crashes. Second one happened while I was running sfc /scannow, it was in the verification stage. After that I disconnected the external HDD just in case. I'll restart sfc /scannow now. Not attaching a health report as I figure those are getting redundant. Tell me if I should keep posting them.

edit2: Alright, I got chkdsk to run for C: on my second attempt, this is what I got from Event Viewer:

CHKDSK is verifying files (stage 1 of 5)...
Cleaning up instance tags for file 0x1ad73.
887552 file records processed. File verification completed.
1291 large file records processed. 0 bad file records processed. 2 EA records processed. 74 reparse records processed. CHKDSK is verifying indexes (stage 2 of 5)...
981396 index entries processed. Index verification completed.
0 unindexed files scanned. 0 unindexed files recovered. CHKDSK is verifying security descriptors (stage 3 of 5)...
887552 file SDs/SIDs processed. CHKDSK is compacting the security descriptor stream
Cleaning up 2719 unused security descriptors.
46923 data files processed. CHKDSK is verifying Usn Journal...
37571664 USN bytes processed. Usn Journal verification completed.
CHKDSK is verifying file data (stage 4 of 5)...
887536 files processed. File data verification completed.
CHKDSK is verifying free space (stage 5 of 5)...
127439054 free clusters processed. Free space verification is complete.
CHKDSK discovered free space marked as allocated in the
master file table (MFT) bitmap.
Correcting errors in the Volume Bitmap.
Windows has made corrections to the file system.

976657407 KB total disk space.
465693176 KB in 383035 files.
186116 KB in 46926 indexes.
0 KB in bad sectors.
1021899 KB in use by the system.
65536 KB occupied by the log file.
509756216 KB available on disk.

4096 bytes in each allocation unit.
244164351 total allocation units on disk.
127439054 allocation units available on disk.

Internal Info:
00 8b 0d 00 90 8f 06 00 4b 60 0b 00 00 00 00 00 ........K`......
10 37 00 00 4a 00 00 00 00 00 00 00 00 00 00 00 .7..J...........
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ................

Windows has finished checking your disk.
Please wait while your computer restarts.

Finally, some test turns up something. After that was done, I woke up to find an error waiting for me:

Faulting application name: sdiagnhost.exe, version: 6.1.7600.16385, time stamp: 0x4a5bc3d4
Faulting module name: mscorwks.dll, version: 2.0.50727.5456, time stamp: 0x4ef6c091
Exception code: 0x80000003
Fault offset: 0x000000000018a6e8
Faulting process id: 0x%9
Faulting application start time: 0x%10
Faulting application path: %11
Faulting module path: %12
Report Id: %13

Fault bucket , type 0
Event Name: APPCRASH
Response: Not available
Cab Id: 0

Problem signature:
P1: sdiagnhost.exe
P2: 6.1.7600.16385
P3: 4a5bc3d4
P4: mscorwks.dll
P5: 2.0.50727.5456
P6: 4ef6c091
P7: 80000003
P8: 000000000018a6e8
P9:
P10:

Attached files:

These files may be available here:
C:\Users\user\AppData\Local\Microsoft\Windows\WER\ReportArchive\AppCrash_sdiagnhost.exe_babb8fffddf9 ba44901a5d8b5c9a63362eb3f12_120d6126

Analysis symbol:
Rechecking for solution: 0
Report Id: 91ef884a-c945-11e1-9e5d-00252246893b

The PC seems fully functional though. I suppose from now on, I keep running Chkdsk till it stops turning up errors, then fix that stuff with sfc?

I did a second Disk Check in the meantime, which turned up clean, so that's something. SFC /SCANNOW found nothing, but the problem with sdiagnhost.exe hasn't reappeared after a couple of restarts. I did get a "Desktop Window Manager has stopped working." message at some point which seemed to affect nothing at all, but random Windows errors are this stage are still cause for concern I guess.

edit: Another crash, a newer, more specific error this time.
According to the internet a 0xD1 dxgmms1.sys error is notoriously a driver problem with nVidia. It does make sense, come to think of it, I hadn't updated my drivers in some time and the timing after I did isn't that far off. I'll reinstall directX, rollback the drivers and take it from there.

Is there a recommended way to reinstall directX? I'm not too sure about all those programs circulating the web. Installed an older version of the nVidia drivers for now.

Attaching the latest dump files.

...and another one. Nothing so far seems to have helped, I'm contemplating just formatting the thing. I suppose the ISOs from digitalrivercontent.net are the way to go? I have an original key, but not the installation disc.

edit: Another one with a new error this time, 0x7E, cdd.dll

Alright, let the verifier run for ~30 hours, got 5 crashes to report. Attaching as usual.


edit: Actually, I think I've found the culprit. When I rolled back the nVidia drivers previously, I skipped installing the audio component, seeing as I wasn't using it anyway. It looks like Windows Update had a different idea, so it updated the drivers for it, to the newest, suspected faulty, version. I have since done another clean reinstall, including the audio component for the old drivers. The PC seems to be stable. I left it running all night and day with Windows Media Player playing music (though turned off speakers) and Media Player Classic running videos, which seemed to be its favorite activity during which to crash (although it might be coincidental, I do watch a lot of stuff) and ~24 hours later, I have no crashes or other errors of any kind to report.

I'm saying all this with restrained confidence, of course. Would running driver verifier for another 24 hours or so be guaranteed to not crash the PC if all problems are resolved? I might do just that, to make sure.