My 1996 Cadillac Eldorado been having problems starting since DVD players instal

Hello, How did you run power to the DVD player and headrests? Is the DVD unit part of the dashboard? Did you ever ground the positive leads for the DVD player or headrest screens to the chassis? These are the types of questions that will help you retrace your steps to find where you went wrong. Check all of your fuses with a test light, and if you can't track down the issue, have it towed to the shop. Unfortunately, this is as much help as I can offer since the issue is a result of modifications, and I have no way of seeing in what way it was modified.