after a power outage serious computer issues, feels like it has no ram.

Hello, I am a relative novice to dealing with hardware, and was hoping for some help.

I had a power outage a few days ago, and since then my computer takes between 3 and 6 minutes to shut down, and forever to boot up fully.

When turned on, the keyboard and mouse light up shortly, but the monitors takes forever.
It took several tries to even get the monitors to power on in the first place, and the first time it did, the right screen flashed black spasmodically, but that seems to have fixed itself.

Once the screens finally turn on, I can do normal things like browse the web, or open programs like discord, chitubox, minecraft and Diablo2 (original).

It will also open steam, but as soon as I click library steam freezes and won't do anything further.

I tried to run several virus scans with windows defender, only once did it actually start checking files, and that froze as soon as I touched another program. each other time it just stays at 0 files checked.
I'm moderately confident it's a hardware issue, but I'm not sure where to start. any advice would be great.

 

Thank you for the response, I did that to both of my hard drives, the first one took 2 hours, and said it was fine, and the second one I let run overnight, so I dont know how long it took, but it also said it was fine

 

I didnt have any restore points, (thats my bad) but i reinstalled windows. the bootup process is faster. I started a full virus scan, left it overnight, and this morning checked it, it said it had scanned about a quarter of my files, and had 35 hours left, then it closed itself. when I reinstalled steam, I had the similar issues as before, as soon as I click on a game, or try to allocate a directory for it to use to access games, steam freezes up and 'stops responding'.

otherwise it feels snappy, like its supposed to. (PS its a reasonably new powerful build from last year)