Ubuntu 14.04 - No Unity in user account, but in guest account

Yesterday I switched back from Linux Mint to Ubuntu 14.04 and after installation I faced the following problem:
When I login with my user account Unity isn't loading. I can see no desktop elements - all I have are the desktop icons in some kind of GNOME-scheme.
But when I login as a guest on the guest account, Unity is working fine.
I read and tried alot yesterday as Ubuntu 14.04 seems to have plenty of issues with lightdm, compiz, ... but nothing worked for me.
I have two asumptions:

1. Because the guest account works, it seems to be an user specific problem.


2. Because the guest account works, there seems so be no problem with graphic driver etc.

To 1:
Are there user specific configurations? Maybe in xorg.conf? Any other explanations why the guest account works fine and my user account does not?

To 2:
I have a Nvidia GEFORCE 520M running. I tried the nvidia-driver, but then no desktop appeared, neither in guest account nor in my user account. So I removed them.

I tried so many things yesterday, so that I absolutely lost track on more possible solutions. Anyone an idea?