Manual 5sp - A pop, now gears won't engage

Last month I had my clutch and slave cylinder replaced due to a hydrolic fluid leak. Car has been running great since then. Then today at a stop light I went to shift into gear and go. There was a pop and the engine just rev'd. Somehow I made it across the intersection and coasted to the side of the road. NO visible fluid leaking, stick shift seem normal, clutch seems normal, no gear - 1st, 2nd, reverse works. When the car is in gear engine revs but kinds sounds like a vaccuum thats belt broke, revs normal sounding when not in gear.