Trying to diagnos and repair intermitent start problem?

95 chevy s-10 blazer 4dr 4x4 w/4.3 automatic w/overdrive. Recently bought has had starting issues, when key is turned to on position the dash lights don't always come on, when the lights do not come on, starter turns over, but will not start. When dashlight come on before start, vehical starts and runs fine. But abs, brake and check engine lights stay on. Abs computer was not hooked up at time purchased and was reciently plugged in. Ingition modual seems to be working correctly, but computer will not connect for a diagnoses. I believed that this is a damage/ corrupt computer, just want to make sure before replacing the computer @ $200.00.