Last night I told my computer to go to sleep and left it as it was doing its thing since it can take a good 10-20 seconds to fully go down into sleep mode. This morning I returned to my PC to find it hadn't fully entered sleep mode. The displays were off, power had been cut from USB devices, but I could hear that the fans were still running.
Wiggling/clicking the mouse gave no response. Pressing keys on my keyboard resulted in no response, other than the keyboard backlighting briefly turning on and then off again (it turns off when my PC enters sleep mode). Pressing the power button on the tower resulted in no response.
It didn't occur to me to try ctrl-alt-del at the time, and I ended up just holding the power button long enough until it fully powered down.
When I turned the machine back on I was greeted by a BSOD before it even made it to the "loading Windows" startup animation. After the machine rebooted itself it went into self diagnostic and ended up checking the disk(s) for errors. Then it told me it couldn't repair the problem.
If I manually boot from my OS SSD from the BIOS (UEFI) I get an error saying something to the effect of:
"NTLDR is missing. Press ctrl-alt-del to restart your computer"
Everything I've found in my searches on the error seems to indicate that this error message is for Windows XP/7 and I should only be seeing it if I upgraded my PC from an older version of Windows to Windows 10. But I haven't done that. I have formatted this SSD and installed a fresh copy of Windows 10 on it in the past.
Other guides I've seen either don't work (probably because they're written for Windows XP/7) or I can't be guaranteed whether or not they'll work since they suggest using some program(s) (usually partition managers) that are not free, and I'm hesitant to buy something that I'll likely only need this one time without knowing for sure that it will solve my problem.
I've booted into a Linux Live USB and the SSD itself seems to be functioning properly and the data appears to be in tact.
It seems the problem stems from the fact that the PC failed to fully enter sleep mode. Perhaps that changed some files or boot configurations and I just need to modify or replace some files somewhere, but so far I haven't found any useful information that is actually helping me to repair the boot problem.
Any helpful tips, suggestions, or pointers would be greatly appreciated.