[xeroinfinity]

This is probly your ignition switch fauling up.

Might try and clean the keyhole with some electrical cleaner.
I have used a paperclip and a tough rag/paper towel to clean it further. Then blow it out with some compressed air.

Also at start up,
if the security light is flashing,
try and wait till it stops before you crank the car over.

But eventually the lock cylinder will just wearout and need replaced.

Hope that helps.