1998 Ford Contour GL

I have a 1998 Ford Contour GL with 93,000 miles. I have had the car for about 1 1/2 years but I have driven it less than 2,500 hundred miles. This is because I can't keep it running. The car will drive fine for two or three days and then it will just stop completely. No ticking, clicking, squeling, or any other weird noises. It just won't move. I have had the starter, fuel filter, head gasket, and a lot of other stuff done to it, to no avail. I have had it tested and they tell me that no problems show up on the computer. Someone told me to check out the fuel cell sensor. What is that and where is it. Or can someone tell me how to fix this car, please.