<font color="blue"> Possibly water in your hydraulic system and it is freezing up. That would be my first thought. </font>
Idaho, this was my very first thought too. By "water in the hydraulic system", I don't mean a big puddle of pure water somewhere, like you might find in the bottom of a gas tank. I suspect that the hydraulic fluid has picked up water throughout all the fluid in the system, and I bet (my usual) $.05 that if you look at a sample of the fluid it will appear quite milky. Your same exact symptoms just happened to my log truck.
What I suggest you do is keep the machine in a heated place until you're sure it's all thawed out. Another $.05 says all the hydraulics will then work fine. Then change the hydraulic fluid and filter(s) and you should be good to go for the winter, with just the usual "morning sickness" to contend with.
I'll bet my last $.05 that the reason it's always been fine in previous winters is that the fluid had not yet picked up enough water to lower its gelling point.
As another poster said, take care of it right away before you hurt your pump, they hate cavitation (and water!). Ditto the rest of a hydraulic system, water and contaminants are murder on EXPENSIVE hydraulic components. Seals, rods, pumps, motors, spool valves, everything.
Lots of other fluids need to be changed WAY more often than they typically are. Funny how we wouldn't dream of missing an engine oil drain interval, but let some things go way over what the maintenance schedule calls for. Brake fluid (every two years at least - it REALLY absorbs water), antifreeze and gear oil come to mind. How many cars are there out there with brake fluid that hasn't been changed in 5-10 years? And think of all the poor, forgotten differentials out there, wearing out long before their time. /forums/images/graemlins/frown.gif
OK, there's my $.15 worth /forums/images/graemlins/laugh.gif