1995 Honda Civic Clutch

My car was driving fine and I parked it overnight outside in bitter cold (below zero temperatures) and next morning after letting car warm up for 15 minutes I could not put the car in gear. I figured, like an idiot, that it was just too cold and got a ride to where I needed to go. 2 days later went outside and let snow melt off car for about 20-30 minutes and still could not put the car in gear. When I pushed on the clutch I noticed that it feels like there is nothing, no pressure, behind the clutch. Wondering what the problem is and how much to repair? I have never had any problems with the car.