Had to look at a manual. You have a transmission that has mountings for two hydrostatic pumps and your hydraulic pump. The hydrostatic pumps have separate charge pumps attached. Depending on ser.no, you have 1 or 2 filters. According to the manual, if the filters clog, no oil gets to the hydros.
It also mentions a screen at the suction side of the tank, and that can cause no drive, but it also slows down your hydraulics.
Your hydrostatic motors are attached to final drives that have clutches and brakes.
You're not the same guy who posted a while back about whether you should buy this smokin' deal 975, are you?......=).
There are a lot of things that can go wrong here. I suggest getting a manual, very first thing, unless you can hook up with an expert.
Good Luck.