1990 CR250 problem with no compression, zilch?

My 1990 CR250 recently died on me after sputtering and limping down the road. I noticed that compression was low but kept riding until it died. also the kick starter jammed on me before and i couldnt crank it. Now I can roll it in 1st gear without the clutch engaged. I realize its probably the top end but is it something more serious like a cylinder? Or do I just need a top end kit put in it. Please help and give me all the info you can. Ive never had to rebuild a 2 stroke. Thanks