no video in video sequence window I've been playing around with blender today, and now suddenly, I'm no lenger able to get a preview window of the sequence editor.

It just shows a black screen.

I have a videotrack so there should(?) be some output.

edit: Suddenly realized there is no audio either.
On the right to the preview window, you have set a proxy size to 50%. But if you don't build a proxy file, the preview can't show you a video.

So either set the Preview render to No proxy, full render, or with you video strip selected, scroll down the strip properties until you reach Proxy/Timecode and make your desired settings. Finally, to build the proxy files, have your strip selected and go to Strip -> Rebuild Proxy and Timecode indices and you're good to go.