Danish,
It sounds like the clutch is slipping. You let go of the lever and the bike just drags to a stop, but the engine doesn't turn over...Right?
Just to make sure:
Remove the sparkplug. Lean the bike over on the kickstand so that the rear wheel is clear of the ground. With the clutch lever released, (clutch engaged like when trying to start the engine)...spin the pedals, by hand or foot.
Do the pedals spin freely?
Can you hear a puff of air coming from the sparkplug hole?
If yes, your clutch is slipping...(with the plug installed the compression of the engine is enough to cause the clutch to slip).
If no, the engine may be locked up.
Jim