What about when you turn it to the accessory position? Do lights, gauges, etc., work? If not, do you have access to a DVM to check the battery voltage? If "yes" the same applies. The easiest thing to check is the condition of the battery. It's not that unusual for something to be left on that drains the battery overnight.
I have a 2003 Chevy Silverado 2500 HD. 140,000 miles, 6 liter engine. I have all electrical systems as normal, but it will not start. When I turn the key to start, I get nothing, no click, anything. My battery is @ 2 years old and I use the truck almost every day for hauling and trailering.