Car wont start but all electrical components come on

sounds like an electrical issue could be as simple as a fuse a bare wire rubbing on metal or loose component check your ignition fuses

Some check light on dahsboard or "theft" system there?

ckeck the starter

These cars and many many many other gm cars and trucks are equipped which an antitheft feature. Many times on engines swaps and ignition changes, this system gets interrupted because the computer is not seeing the proper signal from the original equipment. Try to start the car, when it doesn't turn over, leave the key in the "on" position. Look for a light near your gauges that says "security" or "antitheft". If you see this indicator light, then the problem is definitely the antitheft system. Fixing it is rather expensive. Bypassing it is relatively cheap. This link explains everything you need to know.

http://vatspasslockpasskeysecurityhelp.yolasite.com/

Starter and /or soleniod are dead - replace them and you should be all set

sounds like the ignition lock cylinder has gone bad call a locksmith.

You have a bad starter if all your connections are good and your battery is measuring 12.7 volts and above with engine off.

replace the fuses and check all the wire connections unter the dash by the pedals and under the hood if that doesnt work get your computer checked

Sounds like the battery is dead, you have just enough power to have the lights come on, but no cranking of the starter. Try putting the battery on a trickle charger, or hook up jumper cables to another car which is running. Let it run with the jumper cables connected for two mintues before you try and start your car.