Question: Basicall I have installed a few desktop environments. And if you are familiar with Unity, you know that the way switching works, is you get this sort of drop-down with all the environments installed, you then high-light the desired option and click "ok". So my problem is that I have quite a few installed, and OK button is outside of the screen, and I cannot find any way to scroll down? So in turn, I cannot switch my DE as a result.. any way around this?

Answer: 
I think the problem is that Nemo doesn't start automatically.
To check this, as soon as you log in open "system monitor" and control if "Nemo" is one of the active processes.
If not you should go to "Applications boot", or something similar, and add an entry, call it "Nemo" and fill in as a command "nemo".
Under your system settings you could find default applications settings . there you can change your file manger from nautilus to nemo .

then re login . 

hope that helps .