Just wanted to share how it ended:

I could start it up in safe mode, but whenever I started it up normally it crashed before starting, and then finally crashed (though it could take a couple of...

Will do, and glad to hear that.

Because I have so much trouble with the reboots, I decided to reboot from safe mode into safe mode with msconfig to see what would happen, and it booted and let me...

I let the memory test run during the night, no errors.

I deactivated all startup programs and non-MS services, still crashed (multiple times) on startup.

Booted up in safe mode (with...

Malwarebytes: No threats found
TDSSKiller: No threats found
AdwCleaner: Found no malicious programs
ESET Online Scanner: No threats found

Did the system file check, first time:

Beginning system scan. This process will take some time.

Beginning verification phase of system scan.
Verification 100% complete.


Windows Resource...

No dice there either:

HD Tune: Crucial_CT240M50 Error Scan

Scanned data : 228845 MB
Damaged Blocks : 0.0 %

Oh well, I've managed to exctract the product key, create a Windows 10...

Hello,

Thank you for the reply! I do have an SSD (15 months old), so I ran a Windows 10 chkdsk (Disk -> Properties -> Tools -> Check) instead of the recommended SeaTools, but it came up empty:
...

So I've been using Windows 10 since I was able to upgrade with little to no problems. Then suddenly, on October 8th I think, during a Windows update all hell broke loose. Audio cut out, network...