Just had a blank screen after starting an xfce session which is a bit annoying. Luckily I could still Alt-F2 to start firefox from terminal.

This handy hint by xerodeth seemed to solve it:

” Re: Xfce Session won’t start
so not sure if anyone still needs help with this… but this is what works for me. in your home dir there should be a folder called .cache, go into that folder and delete the sessions folder and the xfce4. i removed both these folders and the desktop came back as well as wallpaper.”