2007 Avalanche won't start

This morning I went out to go to work and the Avalanche will not start. The battery is only about 6 months old. When I opened the door the horn went off once and the lights blinked one time. Also could not jump start the truck either. When I put the cables on no lights came on or anything. I drove it last night and everything appeared fine. Anyone have any input to whats going on.

Wendell