I HAVE A 1998 S10 PICKUP IT CRANKS BUT WONT START.

Kelly, could be a few issues, security lock out, crank sensor, fuel pump fuse/relay, faulty new pump,faulty ignition switch, etc. Attached links may help you diagnose the crank no start issue you are having.
Check the attached links,video,instruction and guides, Good luck
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96 98 Chevy pickup cranks but won start first steps
GM no start no fuel troubleshooting
No Start No Spark Cranks OK GMC Jimmy S10 Blazer

Try turning the key to the on position (do not start) for about 10 minutes or so! This should reset the security which is probably cutting off the fuel circuit! I know GM had many ignition problems with this!

Start out by spraying a small amount of starting ether down the air cleaner. If it cranks and runs for just a few seconds at least, you probably have a fuel problem. Turn the key to "On" and listen: Do you hear a whirring noise, the fuel pump kicking in? If you do, then you need to replace your fuel filter. If not, you may have to replace the fuel pump. If the engine does not start up after the ether, you might check the distributor, make sure all the wires are plugged in. If they are, The coil may have failed.

98 chev pickup s10 put gas in the gas tank drove it about 2days and the check engen light came on had it check mech said it was the gas cap replace the gas cap the light back on now what help

Gas smell. Gas line is rusted through. Look for it all the way back. Since it runs a bit with fuel in the throttle

check to see if getting fuel or if you smell gas when cranking if you smell gas you probably have a spark problem which will probably be a coil and or a pickup coil in your distributor replace coil and then distributor. If you are not getting gas most likely fuel pump in tank see if it will fire on starting fluid then replace fuel pump good luck

ecm more likely

Check the starter relay?

it is located by the spare tire and on the side hope that helps

possibly fuel pump faulty