If it is above 20 degrees, 9 times out of 10 it is a plugged fuel filter. Water, dirt, & etc. This fall we have had a shortage of diesel, & have had _very_ poor fuel quality, folks all across the country are having big issues with bad fuel, clogged filters.
Some newer designs are self-priming, most still need to be primed when you change the filter - or run out of fuel. Read that portion of your manual..... Tractor will _not_ start when you intoroduce air into the line until you bleed the lines......
If it is below 20, it is possible your fuel is gelled. There are products like Power Service brand that will let you use summer (#2) fuel. Or you can use #1 fuel. At your point, if you have mostly #2 in the system, you can buy another product, such as 911 by Power Service, that will soak itself in towards your fuel filter & through the lines. It does work, but is not a miricale worker for all situations. I would put the anti-gel stuff in now, let it work, and try to start it the following day. Changing the filter out also helps a lot for a gelled up system.
It's a toss-up what your problem is, gelled fuel or clogged filter, but the solution is to put in an anti-gel & change the filter, either way...... Dirty watery fuel is a serious problem this year.
I run the farm diesel's down to 5 or 10 below in this climate. This fall I goofed, put in an anti-gell anti-freeze, tractor died on me 10 minutes later. Replaced the filter, ran another 10 minutes & died. Turned out I got the wrong container of anti-freeze, got a gasoline only product, it lowered the flash point of the fuel and broke out the wax so it clumped on the filter. Drained the tank, filled with fresh #2 and Power Service, bled the lines (for the 3rd time, in a 15 degree shed...) and has run since.
It's easy toget messed up fuel.
Other remote possibilities are: Your tank is empty, your fuel shut-off selinoid isn't working, your glow plugs aren't working.
--->Paul