D4 Running in task manager but doesn't open

What did you delete? Can you still recover it from the Recycle Bin?
It’s already late here, I will have a look at the audio engine dump tomorrow…

It was the audio engine from 3.5 which I thought was no longer needed. I have restored it.

Might this be a licensing problem again?

Yes, on the face of it, it certainly looks like a licensing problem – and unfortunately, one you have presumably inadvertently created for yourself by deleting files. What exactly did you delete?

The only thing I deleted was the audio engine from 3.5, then I restored it but that made no difference.

I had a look at the audio engine dump now and it is also hanging while initializing the licensing system. So I also think you must have deleted something more (maybe just by accident) so that it does not work any more all of a sudden.
I’d try running the Dorico installer again. At some stage you are asked to install, reinstall or repair your installation. First I would try the repair option and see how that goes afterwards. If that does not do, go for a reinstallation.
I hope this gets you up and running again.

Thanks Ulf: I reinstalled and that fixed it. Thanks for all your help.

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