Help!!! Truck will not crank!

[lamar]

Started 2 weeks ago, went out to go to the store and it would not start. Checked the basic stuff and everything looked good. Next day it fired up like normal. A few days later the same thing, wouldn't crank. That was a week ago and still not having any luck. It will turn over, but nothing more. Could it be something to do with the little junction block on the inner fender next to battery? I have checked almost everything I can think of. Any ideas ? Brake light is on but don't think that could effect it. Don't think timing has changed. Thanks in advance Lamar.