95 Chevy Blazer Won't Start

I'm going nuts with this car. I need help! It won't start. The battery is ok, starter is ok. When you turn on the ignition the starter engages but the engine won't start. Usually, there is that sound (signalling that there is electricity) when you turn on the ignition but it doesn't make that sound anymore. The headlights work, interior lights work. What's going on here??? Please help. The mechanics are trying to figure out what's wrong and they couldn't find the culprit yet. They say there is no electricity going to the engine? Please help.

check the main ground coming from battery, worst case:( get a good size breaker bar and the rite size socket and see if engine will turn manually at the harmonic balancer