If you are pulling your cub cadet out of the shed for the first time this season and it won't start...it's most likely the battery. If jumping the mower does not help, you may have a bad starter. Here are some brief instructions to check your cub cadet starter:
1) Remove the dust cover from the starter so you can observe the starter gear in operation.
2) Use a set of Jumper Cables and attach the positive lead to the positive post (be sure the battery is either fully charged or new).
3) Firmly touch the large post on the starter. If the starter does not turn, then the starter has gone bad.
A new cub cadet starter will generally run you between $50 and $100 depending on your engine model. Cheaper prices can often be found online.