How to fix my '98 S10 Chevy?

I bought this truck, 6 months ago. The wiring had been messed with. It ran fine for a while, but now, when I turn the key to start, nothing happens. It's a standard two wheel drive. I installed new wiring harness and a new key and lock. I think I reprogrammed the key as instructed. Now, the security light does not flash, but still starter does not engage. My son jumped it at the starter. It turned, but wouldn't start. I shorted the yellow wire, under the switch and it bumped the starter. (We have wired the clutch switch together.) Can I install inline fuel pump and button switch for starter? What about the computer? Since I bought it the lights only worked when the motor was running. Thanks for any help.