Drive belt for belts jumps off and gear shift mec. sloppy

I do love my Yamaha ys624, but this winter some problems started. The gear shift mecanism started to be difficult. Not able to shift from 4 to 3 but beeing wiolent it worked. Getting it into 1 almost impossible. Then, no movment on drive belts at all, no matter first or any gear. Removing the cover in front of engine - the belt pulling the drive belt was off with no damage to belt.
Do I have to dissasembly the hole thing to get the belt back on?
Any tips on why the shift mecanism is so sloppy?
Regards Norway - had tree feet of snow and the snowblower is broken hundred some meters from my garage - upphill-----!