Is it a diesel. If it is, change the fuel filter. There is a possibility it has a water trap type fuel filter. If it does, a temporary fix may come from unscrewing the plastic knob on the bottom of the filter until just diesel comes out. The sludge and water gather at the bottom of the filter, so they will drain out first.
Even if it does have a water trap filter, still replace it as soon as you can, as these need replacing quite frequently on diesels.
If you dont usually do your car maintenance yourself, take it to a garage, as it may have a manual bleed system for the fuel. If it does, when you replace the filter, air will get into the system, and the car wont run at all. One way to eliminate this, is to fill the filter with fuel before fitting, but it does take a bit of skill to get this right.