computer won’t fire up

I added a gig of ram to my wife’s work computer and now it won’t come on. Three times when I pushed the on switch the fans spun for a second or two and then nothing. I’ve pulled the ram and tried it with no luck. I’ve tried two different power supplies with no luck. With one of the power supplies I got the fans to spin but just for a second. What is the next step in troubleshooting?