blazer that won't start maybe a security system malfunction

If it is the security system:

There is a switch on top of the ignition lock cylinder, under the steering column trim cover. You can short the two white or yellow wires, and the vehicle should start.

If it starts and stalls within a few seconds after doing that, then it's in that circuit.

Alternatively, if your key has a chip in it, which is only a resistor. Disconnect the plug next to the steering column, under the dash near the brake pedal. Put a piece of paper clip in each socket in the wiring harness part of the plug (The two yellow wires go back to the ignition switch to read the chip) stick the key between the two pieces of paper clip, at the resistor/chip.

The car should start, unless it's not the security system.