Using the straw attachment on the nozzle, inject aerosol silicone lubricant into the window tracks both sides of the glass and ahead of where the window will slide. Do this on the upper track as well as the lower. Let it soak in, then use something like Draper Suction Pad to get a better leverage on the window. When you do get the window to open, clean the tracks and use the silicone regularly; do the same for all windows.
This is a timely post I managed to get a long stuck starboard window sliding again this weekend and it wasn't by washing or spraying it...
Depending on your window design you might have lumps of salt crystals growing underneath the top track liner like I did... They're almost impossible to see unless you pull the liner down and out from one end.
My driver's window had been impossible to open more than a couple of inches since I bought the boat 7 yrs ago and presumed the frame was warped or binding it was so bad.
Every year I'd try something... Scrubbing with soapy water and long bristle brush, flushing with clean water, graphite powder, silicone spray, WD40, waterproof grease etc.
Nothing worked despite cleaning and lubricating both the top and bottom tracks and liner (alu frame and firm rubber cloth type liner).
After my annual attempt at the above I realised the top track liner was only push fitted into a groove and the end was loose so I pulled it out from the rear to give it a wipe.
I was amazed to find lumpy deposits of salt growing underneath between the alu frame and the soft liner. They were like rock salt and caused bulges in the liner but not enough to see from the outside.
I gently scraped it all out with a screw driver, washed the liner, pushed it back in and hey presto the window started sliding again now the bulges were gone.
Well worth checking if yours doesn't respond to an external clean or lube.
Weirdly the port side has always been fine so not sure why the other one managed to crystalise so much salt...
I'm also guessing it only happens on the upper tracks as the lower ones get regularly washed out with rainwater. The top is under the roof line so salt spray will get in and stay there I presume.