Elevator unable to control

Hi Guys

I'm using FSX with accelerator and a CHUSB 3 lever Yoke with PMDG B737NGX

Recently even the slightest touch on my Yoke and the nose dips and the plane plumets, I cannot get the Elevator to realign in its neutral position

have tried adjusting trim wheel on Yoke but it is impossible the elevator podsition indicator on the FMC controls pg shows the elevator needle either fully up or fully down and cannot be realigned manually and I have calibrated so many times to no use, I recently installed EZDOK and have now unistalled it and reset my defaults but the problem continues with the plane just rocking up or down or falling unless I wrestle with the yoke plane is incapable of levelling off.

In the FSX Options-Controls-Joystick Axis I have

Aileron Axis   assigned to X Axis

Elevator Axis     "              Y Axis

Elevator Trim    not assigned

OPtions- Controls- Buttons/Keys

elevator trim down  keyboard key Num 7

elevator trim up             "          "    Num 1

(all default settings)

In Settings - Controls

Aileron Axis  slider  half position      Null 45%

Elevator  Axis   slider half position   Null 45%

Throttle Axis     slider maxed           Null  zero

Really can't understand it  elevator indicator shows fully up or down and cannot be centred, 

please can anyone advise I really have no clue if I should be using other settings in my FSX to control the Yoke function in this respect

  I'm using a windows 7 ultimate 64bits

CPU Intel 1s 4670  16GB

Graphics  NVIDIA GeForce

GTX 760 2GB

Hard Disk SSD 120GBS

                                                                           Many Thanks

                                                                            Richard