Monitor Goes Black after a while, computer still running

Hello,
So a few days ago my psu fan starting making a loud and annoying noise but I thought i'd change it later since the rest of the psu works fine. I searched it a bit and I changed my power plan so it wont make that noise and it really helped. But for 3-4 days now my computer either restarts on its own or go black after a while while computer is still on, all randomly no matter what i'm doing. I was thinking of changing my psu but could the problem be caused by something else? I don't want to spend money on it and not having fixed the problem.