If the clutch oil reservoir went empty and you just refilled it without bleeding it then you might have an air bubble inside the system. Just unscrew the bleeding nut on the slave cylinder and let the oil flow out while at the same time making sure to keep topping off the oil in the reservoir to avoid any other air to get in the lines. Do this for a while and then finally tighten the bleeding nut and top off the oil in the reservoir to the right level. If that doesn't work then yeah... you probably need a new MC.