2000 Side windo question

I had the same thing happan to my car. if you can get the window up don't try opening it cause it may cause the window to break. here's the bad news. the window is attached to 3 guides and what has happened to your window is that the guides have broken off the bottom of the window which will allow(sometimes) the window to roll don but not up.. attempting to roll the window up causes it to move back and fourth instead of up. anyway, being that the guides are attached to the window you will have to actually go and buy a whole new side window and have yours replaced.
This happens to a number of 99 and up mustangs. it should be a recall but it's not a saftey issue so we're SOL.
It costed me about 60 bucks for everything to be fixed. If you're lucky your mindow motor won't have to be replaced(mine didn't) but when the guides break off the window it causes the mindow motor to blow if you keep trying to raise and lower the window.
If you have your window up look through the little hole in the side of the door to see if you can see the bottom of the window, if nothing is attached to it and it's just the smooth bottom of the glass then you will have to replace it, if you see a guide then maybe you're in luck.
Everytime i looked in the little hole there was a slot that i could put the window back in that would let the windo roll back up(sort of). If there is a spot like that in your door, that is what is supposed to be attached to your window.
If i confused you i'm sorry. i'm not that great at explaining these kind of things. but more than likely you will have to replace the side window and plastic wheel that helps roll everything up. like i said my fix costed me 60 bucks but it may vary whereever you go.
I hope i helped you a little and explained everything ok.

I forgot to mention my car is also a 2000gt. if that helps any

If you have all the guides attached then maybe you're lucky and it just popped off the track or one of the plastic guides just needs to be replaced. as for how to work in there.......i have no idea how the guy who fixed mine was able to do so since there is like 1 little hole to work with.