i just got my new kk 5.5 blackboard and flashed it with x copter firmware for my quad
now when i power it up and arm it, only one motor spins and that too at max throttle
i experienced this with my previous multiwii board too
the board is compensating for any shakes or when i tilt the copter
everything is working fine and i have callibrated all escs..
any idea why this is happening??

When I flash it with some other x.copter firmware ..The motor starts normally at 20%throttle. .but still I am not able to figure out 2 y the others are not spinning

Which firmware you used ?.
I recommend the minsoo kim firmware..only that worked for me, please refer to my earlier thread on kk5.5 for the exact firmware version number.

Yes I used the exact same one this time and the above is happening

Quad or Tri ?

Quad

Updated firmware to X COPTER V 2.9 Xx control KR  by minsoo kin niw the one motor starts spinning at 15%throttle.. but still only one motor is working 

What happens if you increase throttle ?

The speed of the spinning motor increases but still non of the motors spin