How can i get my Peugeot Vivacity 100cc starting again!!!?

hi there i have a peugeot vivacity 100cc and it wont start. i was on my way home one day doing around 35 - 40mph and my bike just cut out and has not started since. i have checked i am getting a spark, i have checked i am getting fuel to the carb and both are all ok, i have replaced the spark plug and also put a new battery on aswell. the piston rings and piston seem to be ok, the only thing i have found whilst checking the bike over is that where the piston arm is there was aload of tiny bits of metal....Looks to me like something has broken inside...could this be the problem why my bike isnt started and what could it be that has broken. i have checked the starter motor and that seems ok aswell....it really seems to me like maybe the crank shaft or something down there is seizing because if i turn the cowl wheel or whatever it is called i get 3 quartres of a turn and it locks up but does still turn when u turn it harder.....is my problem what i dont have compression or is it my crank or something else....please help me with this if you can, thankyou.