A quick list of things...
As TomB_tx notes...Check power to the camera via contacts. Also, check in A and as well as M modes.
Check to see if the mode dial is very loose, tighten the spanner ring if needed
Exercies the mode dial by hold down the white button and move the mode dial back and forth a few times.
Check in 125X if camera cycles correctly... cocked indicator and numbers moving.
Check in B if camera cycles correctly... the same.
Try this... loosen the one screw that is next to the frame count window and carefully wiggle that side of the body shell forward and back a few times... three relay contact are just under there and the contact plates could be oxidized.
For a sort of tour of the insides... visit...
http://mysteryonion.blogspot.com/2011/08/that-is-two-me-super-cameras-now.html