I have a 90' model c/k series truck with a 350 crate motor that I've souped up to around 400 estimated horsepower but recently it just quit running. I replaced the fuel pump and it worked again then the air compressor pulley threw a bearing and I replaced it but now when I try to crank it nothing happens. I took the starter to autozone and they tested it and it came out ok but i replaced it anyway. Still nothing happens i dont know what it could be. If anyone could help i would gladly appreciate it.  

do you have a digital volt meter????  to test the battery????

12.65 volts is a 100% charge..
12.45 volts is a 50% charge..
12.25 volts is a 25% charge...

with the engine running..
14.1 to 14.5 volts is a good
please everybody who reads.. this... do not pull a cable to see if the alternator is working...    digial volt meters can be had for under 5 bucks at most hardware stores for a really cheep model... this is 2008...  pulling a cable lets the charging system runaway for a few hundredths of a second.. this can damage electronics and diodes...

or can you take the battery out and have the az charge it and test it on their computerized tester...      are the terminals clean.....  including up under the rubber that surrounds the terminal... ... hot water works best... a stainless steel tooth brush..  cut one end of the loop of plastic that covers the battery terminal bolt to get it clean underneith..  

The battery is fine...its brand new and fully charged...when i turn the key on everything works fine but its not even trying to start when i try to turn it over  

Neutral safety switch! If the motor doesn't even turn when you hit the key, then it sounds like the neutral safety switch has gone bad, so the computer thinks the truck is in gear and won't let it start. When you turn the key, do you hear the solenoid cick and try to engage?

The other possibility is the ignition switch has gone bad.

When you turn the key, do the dash lights come on?

One more thing, just to check the obvious, see if the motor will turn by hand. Put a brekaer bar on the balancer bolt and try to turn the motor. Sounds silly, but it never hurts to check the obvious.  

Thanks for the advice phill..yes the dash lights do come on, and the motor turns by hand.

this may sound stupid but how do i check the (neutral safety switch)..never messed with them before  

I had a car that acted like that, drove me nuts. Turned out to be the fusable link down on the starter wiring harness.  

the neutral safety switch  is on the top of the steering column at the firewall..

4 wires to it.. only the purple are in the crank circut....    get 2 male 1/4" quick disconnects and make a 2 inch jumper out of 12 or 14 gauge.. pull the purple pairoff the switch.. and patch them together.. this elimanates the switch.. if it is a stick shift it is a white device on the clutch pedal that looks like a trombone...  a rod slides in and out... so the contacts are only jumpped when the clutch pedal is depressed to the floor.......

there are several fuseable links at the starter...       you have to use a test light...

the top bolt on the solenoid has battery power... so every wire off of it should have power...

3 o clock position on the solenoid is the S terminal.. this gets power from the crank position and down the purple wires from the neutral safety switch and the ignition switch while it is in the crank position......  

thanks for the help...ill try that, it is a standard trans