In my experience this could as previous posters indicate, be a hydraulic problem. Since the pedal stuck down, I expect that it is. However, similar symptoms can develop because of a failed pressure plate. I have had a finger break and work it's way underneath the "nest" of fingers and cause the clutch to not release. This would not cause the pedal to stick down.
Look for hydraulic leaks and proper bleeding. If it's a hydraulic problem it may be the slave cylinder, but it could be elsewhere in the hydraulics just as easily.
'84 Euro 240D, 523K miles
'88 300E 5 Speed
'81 300D Daughter's Car
Over 800,000 miles in