I have a 1998 Blazer 4x4 (S-10) that won't start. No trouble codes or MIL. It occasionally starts firing for a second or 2, but then continues turning over - until I move the ignition switch from the start position.
I replaced the fuel pump/filter about 1 year ago. The plugs aren't fouled. It occasionally starts normally after I bleed some of the gas/air/vapor from the fuel rail supply.

 

This sounds like a failing ignition switch.

 

Start with the basics... Is it getting fire? fuel?

 

Replaced the Fuel Pump/Fuel filter. All is well - thanks for the responses!

 

is there a security light blinking? if so its prob ignition switch. You do have fuel, spark, compression right?