Im using Win7, run POD as admin, tried different compatibility modes and installed all new updates, to fix my problem.

P.OD. is running fine, but as soon as I tab out of the game, I cant tab in anymore. I can still hear in-game sounds, but its just not possible to get back into the game. I have close it via task manager and restart the game.

Any ideas what the issue might be?

I think you can't really tab out in this game. It's known issue since the original version came out.

This is a known issue (deadlock in POD's Sound Engine thread).
Install and enable PodHacks. It should fix the problem at run-time.