Peavey Basic 112: No Sound other than buzzing

Hi all - not sure if this should go here or in the repair forum, so my apologies if this is the wrong place...

I have a Peavey Basic 112 amp that I've used in high school. A while ago it stopped working, such that I would plug in and no sound would come out. I revisited the amp recently and again nothing. It powers up and buzzes when I have the bass plugged in. The buzzing gets louder if I turn up the volume (duh), but no sound from the bass. I've tried different basses and cables to no avail. Also, if I touch the pickups, the buzz is less pronounced. Not sure if that helps diagnose the issue.

I haven't opened it up yet since I am not a wiz with amp repair and it's such an inexpensive amp that I don't want to take it in for repairs if it'll cost me more than it's worth.

What can I do to diagnose the problem? If it's just a problem with the input I figure I could just re-wire it but I wanted to know if this is a common issue and what I could do to make sure I know what the problem is. Thanks.