Found this on the net, will give it a shot tomorrow
We started having a problem with the driver side window on our 2004 G35 Coupe. It would roll down, but then wouldn't come back up unless you slammed the door a time or two. Went to the forums and saw that quite a few people have had the same problem. Noticed one in particular that said that you should regrease the regulator before the motor burned out. Well, when I finally went to fix ours, the motor appeared to be shot. It no longer would even go down. I took it apart with the idea of replacing the motor ($282) and possibly the regulator ($95). Before I did that, I took the motor off and hooked it up to a 12 volt power source. There are 6 pins in the connector, two on one side and four on the other. I applied 12 volts across the two on the one side, and the motor turned! Switching the leads, it turned the way. I put it back in the regulator and worked it up and down, no problem. No problem, at least until I let the regulator go all the way to one end, which left the cables tight, and the motor a little bound up. The motor would no longer function.
I took the motor off and then took it apart by removing the housing, which is held on by three small screws. I was very surprised at the amount of dirty grease that was present all around the brushes. I cleaned up the brushes and the surface of the commutator and put it back together. I put it in the regulator and let it bind a bit. No problem, it would come alive as soon as I applied voltage. I put it back in the car, remembering to reset the position sensor, as discussed in service bulletin ITB04-033, and now the window is working as it should.