My computer video won't come on when I start computer up.

Hello,
Hi all hope I can get some simple answer to my question.
I have an old desktop that I recouped from my father. Now I checked it out 2GB ram, good mb and a 2.6 Ghz cup.and just a WiFi card aboard.
I put Windows 7 Ultimate on it, worked fine enough but it was slow. So I decided to upgrade the ram if I could. No couldn't do that right away, so as I had it apart.
I had the dumbest idea why not put a video and sound card in it. And add an extra HD for virtual memory use. Ah ha what could go wrong only take me an hour or so.
Took everything apart and cleaned where nesasary....now I put everything back together....started up fine no video.
Did the whole beep thing etc. Have no beeps but still no video. Even took out ATI 512mb rage card out still no video.
So 8hrs later I decided to post to Tom's

Need help

Dr. Bob