Thank you for your help!
I wanted to inform you, that the recently bought USB drive I was using is faulty. Probably the problems with booting lxde and such came from that. It's now on RMA.
Also, I got another question:
Do you think you could make proxmox ISOs work out of the box?
This distribution is debian based. The setup hangs when trying to start the install script. I have to follow these instructions for making it work everytime:
Subject Re: Re: Re: Re: Re: Re: Many Booting Problems