will not power on unless battery and Magsafe are removed and reinstall

Hi I have a MacBook Air Mid 2011 the only way I can get it to start is if I unplug the Magsafe adapter and then disconnect the battery. which is a pain as you have to remove the base.

I then reconnect the adapter and the Air will start. I can also reconnect the battery and that charges ok. I also can remove the Magsafe once running and the Air runs on battery fine. It will also restart on both battery and Magsafe ok, it only wont start if I shut down.

I have installed a new IO power input board all ready with the same result.

I have tried the shift+con+opt+power does not work

I have tried nvram as well.

Have tried resetting SMC as well

I have also run all diagnostic test which reports no problem.

I have updated, reinstall OS done a clean factory install still no good.

Any help would be greatly appreciated

Thankyou

Doug