Need Electrical help!

[Longhorn Man]

I was thinking the same as hotrod.... a bad ignition switch.
Next time it does this, look at your amp guage (which is supposed to move when there is a load on the battery and no alt charging it)
If the needle doesn't move when you turn thye key, then you are not putting a load on the system...hence, no signal to the starter.
if the guage bottoms out when you turn the key, then it is under extreem load...as in, a starter workin on leaving you stranded.
You could go to auto zone and have them test the starter for free...but they just want to sell you a starter. (DON'T get a napa starter) so they may not be the best ones to tell you if you need one.