Could be the starter. Mine would just click recently when it was real cold out (less them 10*F), I could jump the starter to get it moving then start it with the key. Was a strange hard to pin-point problem. Every time it sat in the cold for a few hours would have the same problem. I eventually took out the starter and disassembled it. Found one of the six brushes was not being pushed in by its spring. Haven't had a problem sense.

Most likely a problem with the ignition switch, neutral safety switch or clutch switch if manual and starter selinoid if your not hearing any clicking when you try to start it.