You have a faulty clutch. If you can shift all gears with a dry transmission, but the clutch won't disengage, your issue is in the clutch system. I have seen the pedal assembly mentioned earlier several times, but if you are sure that is not the problem then it is your clutch. The disk may be installed backwards, or maybe the wrong application and is wedged against your pressure plate. I have seen both and they resulted in the issues you describe. In either case, the only way to find out is to pull the transmission and inspect the clutch assembly parts.