It has been said in other threads that many times the reason activation can't be done is because people turned off essential services in Windows that are required by the NGX.

I broungt pmdg 737 on 5/8/2011, to day is 17/8/2011, I have problem with activation. no activation window at all, contacted pmdg via support tickets they have sent me external activation ultility, but still does not work, change my window language to US, but still does not work. I has been two weeks now i am left with "useless pmdg737NGX" sitting in my computer. Just wonder anyone out there has the solution. - PLEASE HELP anyone??Thanksken

I broungt pmdg 737 on 5/8/2011, to day is 17/8/2011, I have problem with activation. no activation window at all, contacted pmdg via support tickets they have sent me external activation ultility, but still does not work, change my window language to US, but still does not work. I has been two weeks now i am left with "useless pmdg737NGX" sitting in my computer. Just wonder anyone out there has the solution. - PLEASE HELP anyone??Thanksken

This might work for you ... http://forum.avsim.net/topic/355872-activation-issues-this-time-with-a-sxstrace-of-the-issue/

I have same problem with activation. no activation windows after the reinstallation.

ticket has been also opened. 

After hours of research, I figured this out. If you are still having this problem today, download service pack 2 for fsx, as the 737 by pmdg seems to have a problem with service pack 1. You will need to activate fsx again though, but I guess you could always find a crack for it on the internet

I also have the same problem, its like the screen are black and no buttons work, the engines work though