Well you have probably had the problem. Put the window down, cracking noise then nothing, no up, no down, just a horrible noise.
Door card off, look inside and either the regulator wires are twisted or the plastic guides on the end of the guide rail are snapped.
Contact local dealer, "no sir, not available as a seperate item, new regulator needed, yes I did say £360"
Look on e-bay. Buy new wires (If only wires broken) refit onto motor drum, skin fingers, swear, loose wire tension etc. Cost (£11-15 and some skin and time)
Look on e-bay. Buy brand new regulator kit (upgraded non Renault part ), remove door card, take out old regulator and motor (3 nuts 2 bolts) fit new unit, electrical connectors different so cut connectors off and fit spade connectors, refit card, job done (£60 and 30min)
As the wire and the plastic guides were both broken, I went for option 3. Looking at the unit it is much sturdier, the guides are wheels not plastic curves, the wires are stronger and 1 yr guarantee.