I was probably using version 3.4.1 (because it reminded me that I could update to 3.4.2). My theme was Twenty Eleven and I tried installing a new theme: Oxygen. The message was: installation succesfull, but my whole site is now white. So, I cannot acces any plugin to restore or undo anything!
I did make two backups (one online and one on the server) so hopefully I can restore my wordpress.
I hope somebody can help!
Kind regards, Rozemarijn