I changed out the steering column in my 1999 silverado now it will turn over but will not start.its getting gas but no spark from coil packs and security lite is blinking. how do i find problem

You have to bring it to a GM dealer and have them link up the ecm on-line to reset the security code (pass lock). The steering column has a security feature as an anti-theft device.

You will have to "relearn" the new steering columns key tumbler code. Follow the steps below exactly and the new code will be accepted.
Make sure you have a battery charger on the battery so the truck battery will not drain. If the battery goes dead, you will have to start over. Read the instructions below carefully and follow exact.
1st, Turn the ignition switch to the ON position, DO NOT attempt to start the truck. Leave the key in the ON position for 10 full minutes.
After the first 10 minutes is up, rotate the key to the OFF position and leave it there for a count of 3.
2nd, Turn the ignition switch back to the run position again for 10 minutes, again DO NOT try to start the truck and leave it in the ON position.
3rd, You will have to repeat the same step for an additional 10 minutes. This will be a total of 30 minutes. After this final 3rd step, turn the key to the OFF position for a count of 10, then turn the key to the start position and the truck will start, the key tumbler code is now relearned to clear the theft mode.
Good luck.

Under dash on steering column theres a wire harness u have to reconnect this to key cyclinder this is common for forgetful ness

YOU NEED TO REPROGAM KEY FOBS