[JRTJH]

The seals are stuck (sticky) and won't release to allow the window to open. I'd try turning the knob as far as it goes (easily) then go outside and use your fingers to pull outward on the window. That will usually release the seals and then you can go back inside and finish by using the knob. You might want to spray some silicone on a paper towel and wipe it on the rubber seals before you close the windows for an extended time.