Why would 96 Nissan quest run great 3 or 4 days then suddenly not start w lights radio etc work great but nothing from starter but if it sits will start next day w no problem?

I don't know the weather conditions where your car lives, but if it's cold enough you could be having trouble with fuel line icing. Small amounts of water can freeze in the fuel line, then fuel can't get through. That's only a problem if you live in parts of the country that freeze. If that's a possibility for your vehicle (freezing) get a can of fuel line deicer and run it through every time you fill up for a month or two. Water doesn't necessarily come from the gas station. As often as not, it comes from condensation INSIDE YOUR TANK.