Why won't my car start, or even more important why did it just die while running?

Hi, I have a 1997 Ford Escort LX, I was coming back from work the other day and as I turning the wheel to get into a parking spot it died, fuel filter was replaced after that, battery (new) was put in less than 6 months ago as well as an alternator (used), all the lights work, the spark plugs and wires were changed about 1 year ago, and the air filter was changed about a year ago, it does turn over but it sounds a little weird. It has had a trouble light code for 6 months (P0401) which is an oxygen sensor but I don't think that would cause this problem, also after I tried to start it a few times after it died the clutch lost a lot of the spring in it. It seems like I barely have to put my foot on it and it would go down too easy, could someone please help?