Why won't my Poulan pro riding mower go into gear?

I bought this used 14.5 hp mower that ran great. We drove it into my truck. I unloaded it manually because it came without the battery. I unhooked the broken mower deck. Replaced the battery and back tires. The mower starts right up and sounds great... But won't go into gear! I've checked the belt, and the e-brake/clutch. I'm not sure if I disconnected something when I took the deck off, or if there's another safety feature that I'm not aware of??? Thanks so much