start with simple things first...

check the battery compartment for moisture or outright water damage.

then, there could be chaffed wire, but less likely, given your symptoms...

also, a weak battery - if the battery is old, or has been discharged more than once, you might want to start with a fresh battery... Also, while seems to be obvious, check battery terminals for loose connections...

let us know about the results, and then we take it from there...

Good luck