jivas

I purchased my truck new in 2001. It is a 2002 ford f150. i had an auto starter installed. i had truck parked for a few months with no use. when tried to start up, the battery was dead. no surprise there, but the auto start never worked after that and the alarm horn had to be disconnected because the thing wasnt working properly. I checked all regular looking fuses, but none were blown. Is there another fuse or module that I need to check? How can I repair this myself?
I would appreciate any and all help. Thank you kindly