BR6108 not flying
 

i have a cheap 3.5 ch heli only took off once and crashed also in this one time , after that its not flying , when i use the remote and go half speed the lower blades goes really fast while the upper blades stays still , then when going full speed with the remote the lower blades speed decrease and the the higher blades start rotating also but with low speed not allowing the heli to take off , any ideas ? i bought it to practice flying before going for higher models , any ideas please