It's quite possible that the runners have got a bit sticky and the one-touch mode has been deactivated. Try spraying a silicon or PTFE based spray into the window runners to lubricate them. Don't use a WD40 type penetrating spray as this can sometimes swell the rubbers making it worse.
Now press the switch so that the window is fully open, release the switch, then hold it down as if ti open it again.
If this doesn't work try it the other way. Close the window, release the switch, then press it as if you're wanting it to go up again.