I sure hope you guys can help me out, here! I've had this problem in the past before, and it was also sometime after I had used the Steam client. I was apprehensive about using it again, but chalked it up to coincidence since the problem had been fixed / gone away without any removal or tampering with Steam.
So, earlier today (or maybe it was yesterday; I've been up many hours at this point), a friend gifted me a game on Steam, I redeemed the code, launched Steam... And noticed it was downloading something it wouldn't divulge without my permission and against my settings, without telling me what it was. I was annoyed, but decided to just assume it was trying to update itself or something of the sort and proceeded to initiate download of the game. Once I was done, had the game installed, put Steam into offline mode, and exited the program it then behaved well in offline mode, only launching to quietly run without using my bandwidth whenever I played the new game.
Afterward, without a restart - which I regret now but didn't honestly consider - I also downloaded my freshly-purchased copy of the game Wolf Quest. I did not use Steam for it, and instead used the itch.io purchased version. It stalled during download, failed, then succeeded when I tried again.
Hopefully this isn't useless information, it's the only change - aside from making restore points along the way, as I always try to do when adding new software - made since a point when my computer did not exhibit the BSOD behaviour now happening.
After a long day of playing and browsing the internet etc, I made sure Steam was not running and rebooted my machine after finally remembering that's a good idea when installing new software. Afterwards, I let the system load, then shut it down as I usually do with the power button. Remembering I'd had a similar issue in the past, I got paranoid (apparently with good reason) and after it was fully shut down, attempted to power it back on.
Cue a stall right at the display of my user icon on the Windows Login screen, cut to blue screen, and reboot. Once it rebooted, it worked well enough, minus large amounts of disk activity related to ntoskrnl.exe ... incidentally also what a tool called Bluescreen Viewer claims is related to the problem. It now crashes every time I turn it on after a shutdown, reboots itself, then (knock on wood!) functions properly until shut down again.
The one time I managed to catch what the blue screen said, it mentioned page_fault_in_nonpaged_area (rtwlane.sys).
I've attempted a chkdsk - no problems found. And I did a sfc /scannow which repaired a couple problems and said that some couldn't be repaired... which i vaguely recall as being unimportant printer-related services anyway. I also attempted to disable page files, reboot, re-enable it with the same settings, then reboot again. Didn't fix anything. I even went through the vague steps which were done with another forum (running CCleaner, for example) but this time it did not fix the problem. Sadly, I've exhausted all the self-help I can and now seek help from people who're far more knowledgeable than I am.
Any and all help would be appreciated, as it's super scary having my system crash every time I start it up, and surely can't be good on its health!
Also of note: please don't ask me to run Windows Update
I also do have restore points from before the games were installed etc. but of course I don't want to have to get rid of the games my friend and I just purchased if it's at all avoidable.
Thanks in advance for helping, and I'm sorry if any of the details provided were unnecessary.