'94 SL1 Wont shift gears while running.

I have a 1994 SL1, manual transmission. I went out to start my car yesterday morning and it woudnt shift out of reverse. When the car is running, I cant shift in or out of any gear but when it's off it doesn't have a problem. Also, there doesn't seem to be any pressure in the clutch at all. The past week or so it has been slightly difficult to shift when we first started it but after it warmed up it shifted fine. The clutch fluid was a bit low however after filling it, the problem didn't go away.