transmission won't go into gear! Help

Having problem with my son's 96 Bonneville. Car shifts into all gears, (automatic) but won't engage, acts like it is in neutral. Very strange, no prior transmission problems, almost seems like a switch or electrical.

Just recently, we did have that wierd electrical problem that others have had, involving the fuel pump and electric windows. The mechanic ran a new ground wire to correct the problem. Car ran fine for 2 weeks. Now this. Otherwise car is in great shape.

Got the car back yesterday from the transmission shop. Needed new parts in the torque convertor. Shaft had broken off. $2000 repair. Mechanic said this wasn't a common problem for the Bonneville, just happened somehow. Hope this is it for a while.