My Computer wont show anything on screen

[Cromagnum_1]

Ok so my computer was running a little slower than usual. So I decided to do a full clean out. Took everything out clean it all up, like I've done a hundred times before. However when I put everything back in 2 problems occurred. My computer turns on and everything lights up and all my case fans are running. But my CPU fan isn't and nothing is appearing on the monitor. I've even tried to use a VGA cable instead of my HDMI. I've checked all the cables everything is where it should be. Any ideas?

 

[hang-the-9]

If this started after you took everything out, you did not put something back in properly. No way to tell from here, have someone else look it over in case you missed something.