@Stovies I have sort of been able to create the screen you are seeing. It is unable to load the defaults. The only difference is that when that happens to me there is a popup that asks to create a new or load the defaults.
Please go into the PSE settings and pick a different folder for the content, click "update content" and then click "ok." Don't put any content into those folders yet; just go to the sequence editor and see if you have the same results.
That should at least narrow it down to whether it is an issue the content or not.