Nikon FG multiple problems?

I bought a Nikon FG from a friend the other day and i was having problems with the mirror going up when it wasn't in m90 or B i replaced the batteries but the problem still continues, any suggestions

If the problem persists the most logical conclusion is that the batteries aren't supplying power.

Have your "friend" help you with your problem

Here is a link to the user manual to help you with your problems.

http://www.butkus.org/chinon/nikon/nikon_fg/nikon_fg.htm

My guess is that you have never attended a photo class, so can't troubleshoot your problems

Sticky mirror. Have it serviced by a qualified technician. While there, request for a CLA (clean, lubricate, adjust) to put the camera back to serviceable condition.