http://www.sqvision.nl/dump/screenshot_vegas.jpg

Please check this screenshot.

I must have done something really wrong. I used to have my preview in a separate window on the right but now it's just a tab. This results in for example no preview visible when using the trimmer. Quite frustrating to edit in this way. I tried all options in the menu and still can't find it. Someone knows how to get the separate preview window back?

Easily done - click on the preview window in the area of the five dots at the upper left, hold, and drag it out to wherever.

Yeah, what Seth said. Then when you have your layout set up exactly how you like it I would save it as a custom layout. (View>window layouts>save layout as)

Yep, That was the solution, fantastic! Thanks for the help!