Please Help: Crank, but no start

[Twisted Illusionz]

I am having a problem with my 05 z71 suburban. It was driving fine, shut it off after getting home from work. Went out a couple of hours later and now it will crank and crank and not start. If I stop trying to crank it and go to try again it won't even try to crank. Then if I shut the truck and lock it, then unlock it allows me to crank it again, but only the one time. I tried scanning it, but it shows that it can not communicate with the ecu. I'm thinking new ecu, but would like some suggestions please. I checked all grounds and fuses already.