1990 Volvo 760 No start in cold weather

Sitting for that long. You should have put fuel stabilizer. The fuel must have degraded.

A fuel flow/pressure test will put that discussion to rest. Lol Need to do some basic tests when it wont start, fuel pressure, spark. Once we know what is missing we can begin the diagnosis, car sounds a little new to be having much debris in the tank unless there was some water damage or the such

I must of mis understood I thought he said it was sitting for 4 years.

When you say it would not start do you mean it cranks over and will not start or it won't crank over at all

As suggested earlier by Mr. Jack on fuel and spark test-do below below and see what happens when it refuses to start, something has to give between the two-

Get a carb cleaner and spray into the carb or the throttle body on an EFI. Did it start and die? If not disconnect a sparkplug wire or 2 and ground it to the engine -have helper crank engine over-do you have a snapping blue spark? If so-you have a fuel problem, check the fuel pressure to rule out the fuel pump/pressure regulator and listen to the injector/s are they pulsing or hook up a noid light.

Fuel pump and Injector/s checks out-start checking the ignition system-power to coil, coil/s itself, distributor pick-up, control module, Cam and Crankshaft sensors.

If both fuel and spark is present-check the valve and ignition timing, this will lead you to problems with compression and valves opening and closing at the wrong time

Ignition
https://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm

Check fuel pressure go here:
https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm

To put the water in tank to rest I would drop the tank, clean out the lines, new filter *again*, run some through the fuel rail to get all water out.

As you said it sat for 4 years? I wouldnt run the gas that was in there through it.

Get all that cleaned out and if it still continues to have a problem on cold weather, then the problem is not frozen lines.