Security Light comes on and off.

Hi, I am new here. I have a 2000 Silverado Z71 LT. I am having problems with my truck consisently cranking on a daily basis. One day it will crank and run perfect when all of a sudden the security light comes on. When I turn it off and let it sit for an hour or two I come back and all it does is spin over. I have tried resetting it by the battery, didn't work. They only way it cranks is if I leave it sitting over night and come and crank in the morning and it runs fine until the next cycle of me letting it sit after I just drove it. I have read a couple of forums making me think it could be the ignition screwing up but would like to be sure. Much thanks for anyone who could help.