1993 320i Electronic Issues

Ok, So I bought this car from the tow yard I work at about 2 months ago. The problem I'm having is that this vehicle keeps on resetting it's electronic components. What I mean, is that I installed a new stereo because the old one didn't work, and I setup the clock on the dash (underneath the stereo). Sometimes, it will randomly reset everything (including the trip odometer). SO i'll walk back to the car, start it up and everything is reset, no clock, stereo settings back to stock, and the trip odometer back to zero. I did sit in the car with the key in the ignition one time for about 2 hours waiting for someone, and the car kept beeping. I don't know if the two issues are related, but I already checked the battery to make sure it was tight, so anyone else have a solution?