Broken window balance has window stuck
I may not be able to tell you who the manufacturer is, for the letters you found on the glass may be the insulated glass manufacturers initials, not the window makers. There should be someplace on the window, a window manufacturers label or something.

The window, since the ballast has broken on one side has in essence, has tilted to one side, even though it may not be obvious. The ballast is trying to lift one side and the window, being quite heavy is wanting to stay closed on the other side. 

To counter effect what the window is wanting to do, you need to push up on only the side the ballast is broke, and pull down on the side the ballast is working. Of course you need to push up harder than you are holding down the other side, or it won't work. Depending on how bad it is jammed, you may only need to push up on the upper corner where the frame (sash) around the glass give an edge to push up by. You may also need to pull down hard on the ballast side to set the window down all the way, so you can then try the other things I mentioned earlier.