2001 SSEi, been sitting about 6 months, won't crank

[Oldman]

I've replaced my Bonneville with a pick up truck, and it's just been sitting for about 6 months. I charged the battery and decided I'd get it running for someone who needs a car. I turn the key and absolutely nothing happens. Battery is fully charged, lights don't die, but it doesn't even try to crank. No "click" or anything. I have 2 keys and tried them both thinking it might be a chip problem, but same thing with both.
Any ideas folks?
Thanks,

[AJT2004]

The battery could be weak although it's fully charged. Connections clean and tight? Did you try a jump/boost? If that does not help, try tapping on the starter.

[Oldman]

Yeah, I'll give that a try. Basic stuff. I was thinking too much about electronics instead of basic electrical.
Thanks,

[maxi426]

The battery could be weak although it's fully charged. Connections clean and tight? Did you try a jump/boost? If that does not help, try tapping on the starter.

This ^^^. Try tapping on the starter while someone else is turning the key to the start position.

[Oldman]

Will do. That means I'll have to air up the flat tires!