bak wheel wnt move?

i dnt no alot about mopeds but i baught i gilera runner sp50 a cuple of weeks ago and i passed my CBT yesterday and my pack wheel started jolting when i went bak out on it n evntualy i cudnt push it whatsoever the wheel was copletely jamed unles i put revs on it 4 it 2 move

can ne1 help if so answer her or add me on msn

scragg_2kaii7@hotmail.co.uk