Can someone explain why my PS4 isn't working?

So I bought a used PS4 a few months ago and the fan was incredibly loud. I dealt with it for a while but then I wanted to try and fix it. I opened it up, cleaned up the fan, put it back together, and then when I turned it on it said it was checking system storage status. It gets stuck at 13 percent for a while then moves up to 29 and then blacks out. I thought i put everything back how it was but I must've screwed something up. I can't send it into Sony cause there is no warranty. Has anyone else had this problem?