First bet is your battery is dying or needs to be charged due to non use. Hearing only a clicking noise points to your solenoid activating but there not being enough juice to turn over the starter.
If your battery is lower than 12v charge it up slowly. If it's dead replace it. Once replaced/charged, then you need to do a few things to make sure your charging system is working. I do a quick test here at the house with my multi meter. Place the leads on your battery. Check the voltage. Turn the key on and start the bike. Check the voltage at idle. It should be slightly more or about the same as before you turned on the key. Then rev the engine to about 4,000rpm, the voltage should rise about 1.2v. Hopefully you'll see voltage somewhere in the 13.0-14.4v range. If so that helps to rule out other charging issues. You might have a ground short that slowly discharges the battery when you don't ride.
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