I got 1997 Corolla DX.

The remote key used to work and alarm too.
1 year ago, I locked the door when the doors are
still open. And I think after that the alarm stop functioning properly

Quite recently, I need to replace the car lights. I had to unplug the batteries.
After plugging back, the remote key stopped working.

CD player too, has very very dim lights (maybe the cd player is spoiling, and has nothing to do with battery)

anyway I could check and fix this on my own without going to professional?