My 2004 pontiac grand prix window it will go down

Does it try to come up, EG is there power being applied when you press the UP switch? if it makes no sound or movement when pressing the UP switch it is probably a worn out switch - available at Pontiac dealers though you may have to order it and wait a few days - have your VIN number for the parts desk and you'll get the part in no time - the switch levers out of the panel - use a plastic tool if possible to prize the switch out so you don't damage the surrounding trim - the cable connector clips off the old switch and goes on the new switch, press the switch home into the recess and jiggle it a bit to make it dead flat - window should work now.
If it IS making an effort to come up then either you have a poor earth or power connection making it so there is not enough power to pull the windows up (which is harder than down due to the weight of the window) -- check the cabling behind the door panel, and as above pull out the switch and check its connector too.
OR... the window is out of alignment and is jamming - putting it back in alignment means taking off the door panel and getting at the bottom of the window runner, loosening the bolt(s) on the bottom of the runner and moving it sideways so it hold the window steady but not tightly, you may have to try having it tighter or looser against the window till you get the best performance - also oil the moving parts/cables of the window mechanism (dont get oil on the glass, it will smear for weeks) to give the best chance of smooth operation.

Just had this happen to me. There are pieces of plastic on the upper and lower side of the bar that helps guild the window up and down. Also the cable is sliding on these two plastic pieces. My bottom one broke. Now i have to find out the name of that piece and replace it.

Needs a new mechanism ,or the door panel taking off to have a look at least