I accidentally left my keys in ignition overnight - and now nothing. Have charged battery and tried spare key, but neither fixed the issue.
First step, remove, clean and reinstall the battery terminals. Check the fluid level in the battery (if possible)
Slow charge the battery on the lowest setting (not the "maintain" setting) overnight.
it really sounds like a dead battery. If you are 100% sure that the battery has juice, my next guess would be to a) check terminals as Larry pointed out and then b) check the fuses.