1997 Plymouth Voyager Hard Starting

My Voyager has been running great, but a couple of days ago, when I tried to start it, nothing happened when I turned the key. The dash lights when on, but the van wouldn't start until I pressed the gas pedal. Took it into my mechanic who said I was almost out of oil ( I had checked it fairly recently) and there was gas mixed in with it. Added a couple of quarts of oil and stuff to help it start - ran well for a couple of days. Problem is starting again and the oil level is low again. They mentioned something about replacing the computer, I'm hoping it's a module only. Any ideas? Thank you!