Open the back and lok above the take-up spool. There is a groove that acts as the light trap for the door. Inside that there is a small "button" like thing. Say 4mm long by about 1mm thick. When the door opens, this button resets the exposure counter as it pops up. I know if this is up all the time, the counter will stay at zero and the advance lockout won't engage. If it is down all the time, the counter should get stuck at 36+ exposures, and the lockout will still work.

Make sure that this button is free to move and that the door is closing enough to push it in and reset it.