No start

2003 Silverado won't start. All the gauges and radio come on. But as soon as I turn the key the radio goes out and most gauges go dim(except engine light) and nothing engages. As soon as I let the key goes the lights and radio all go back to normal. I checked fuses and they seem to be good so I'm guessing the starter or a wire. Any help diagnosing would be great. I'm trying to sell it so rather not spend any more money then I just have too.

Dead cell on the battery?

I'm with Jason on this, dead cell or cells on battery. One battery or two?

Check cable connections at the battery first.
Corrosion might have set in and looses connection when any amount of current is applied.

Ignition switch is my prognosis .

The battery is only a few months old and fully charged. It doesn't make any difference if I try to boost it off so I don't think the battery is bad but I'll double check the connections.

Radiator cap.
Take it off, drive new truck under, re-install, fixed.

I don't want this one much less buying another to replace it with.

Diesel Dan wrote:

Radiator cap.
Take it off, drive new truck under, re-install, fixed.

Finally got warm enough to mess with it again and after a second time hitting the starter with a hammer it started up 3 separate times so that's the problem. Now to get a replacement and change the oil covered sucker.