Welcome to HEF. Did you put the chains back on yet? I would see if the small drive gear will turn without the chains on. I have an 875 that I just got this summer, still working the bugs out, but it's getting there. I also have a 580B that I've had for several years. I don't know if you have manuals, but it helps to understand how the systems work and how to troubleshoot. It could be a few different things. I don't know how familiar you are with Insley machines, but the propel (drive) system has three levers. The one on the left of the seat is the forward/ reverse lever, this just drives the transmission (gear box) in one direction or the other. The two on the left side of the seat are the drive engage/ disengage/ brakes. Pushing a lever forward simultaneously disengages the drive gear from the jaw and applies the brake on the corresponding track (left lever- left track). Moving the lever to the rear releases the brake and engages the gear into the jaw. If you already know this my apologies. When working the brake levers, you should hear the engine labor a bit after a few seconds, this will indicate whether the system is getting hydraulic flow. Since you've had it running and operating, I assume there is enough hydraulic fluid in the tank and the pumps are working. If it's not a hydraulic issue, you might have to take off the belly pans and look underneath. There are two hydraulic motors connected to a drive transmission (gear box). Out of the drive transmission there is a gear-and-jaw mechanism along with brake bands that work in concert. If the brakes have been applied the gear and jaw will (should) be disconnected. The drive transmission can still be engaged and turn, but if both brake levers have been activated there is nothing connecting the transmission to the drive gears. There are other possibilities, but this is long enough to get you started. Post what you find out and we'll go from there. Good Luck!