Dell Optiplex 9010 turns on but does not display anything

[GarytheGeek]

I have a dell optiplex 9010 SFF that i opened up to blow the dust out. i put it back together and plugged it in. it turned on on its own but it does not display anything. Fans spin, Hard drive spins, lights turn on, CD drive spins (which i can also open by pressing the button) but nothing comes on the screen. i plugged the monitor and cable into another PC and it works just fine. i tried swapping the RAM, which did nothing. i tried restarting the computer multiple times and still same result. the computer does not beep any codes. i have a 2nd identical computer and i am very tempted on opening that up to see if i did something wrong but i am afraid that that computer will also stop working. is there something else i can try? i would like to keep it working if i can, but it is 4 years old.