System taking days to boot. Runs great until restart needed.

Firstly, let me apologize for not having any specs at the moment. The PC in question is currently on hour 22 of its boot up. I'll try to describe the problem as best as I can:

When I go to start my PC, I get a power light, and some minimal fan sounds, but that is it. The power light will remain on solidly and I'll get no other response from the computer for days. I get output to the monitor (no bios info, just 'no display' message), but I have power going to my keyboard and mouse, as evidenced by their lights.

It will remain in that state for about 3 days, and then I'll happen to notice the power light blinking, which means it's ready to go. The computer runs like a charm at that point, and will do so until I restart it for an update, or we lose power or something.

I read a similar post from about 6 months ago, and my next step is to try Kyhi's recovery tool. I'm curious if anyone has any input on that, since my system does not show any signs of wanting to boot up initially at all.

That's enough out of me for now. I'll get if I can think of anything pertinent, my system boots up (allowing me to post spec), or to answer questions.

When was your computer last working normally?
What hardware or software changes have you made recently?
Which operating system version are you using?
What is the computer manufacturer and model?

Place your computer in safe mode with command prompt and run sfc /scannow.

Does you computer have UEFI diagnostic studies to run from the bios?

Do you have your files backed up?

A few months ago. I initially thought it was just broken.

No new hardware or software.

Windows 10, current updates.

Not sure. It's a Newegg slap-together. (Promise I'll get more info once it's up again)

Can't troubleshoot right now. Not until it's up again.

I have nothing backed up, but I have nothing crucial on it I'm worried about.