PC's problems escalated, not sure what to do

Hi, recently while playing Dead By Daylight the game kept crashing. Green lights flickered on the screen and then a rainbow strip appeared followed by a black screen. I couldn't get more than 10 minutes of gameplay in. Other games, like Fortnite, I could play. I tried updating my drivers to the newest ones, that didn't help. Today the green lights started appearing outside of the game, while having Steam open. I tried changing out the HDMI cable to no avail. I decided to get the most stable drivers for my GPU (1080ti) but before I could my PC crashed, again green light appeared, the whole sequence happening again, but now i wasn't able to do anything. Then my PC restarted itself three times by itself, but didn't turn on. After trying to turn it on myself, nothing happened. So I waited a bit, the PC turned on, but the resolution locked to 1280x1080, while my monitor is 2560x1440. I tried to restart my PC. It again restarted itself three times, but didn't turn on. Again I was unable to turn it on. Any tips? What should I do?

I bought this PC used about 8 months ago, it worked without any problems until today.