I'm new with Ubuntu and I'm scared to mess around with drivers, as every single time I end up with an unusable system and I have to reinstall the OS from scratch.  

I've installed Ubuntu yesterday and, despite some big issues with the network adapter, the menus, the fans and the sound card, it seemed to work almost perfectly.
But after a restart I got this result: 

![image](https://i.imgur.com/HSIdzQw.png)

(that's the desktop with just an instance of `monkeysearch` in the foreground, the other windows are only artifacts). 

Now it always happens, even 5 minutes after reboots. Here is the desktop right after a reboot: 

![image](https://i.imgur.com/HSIdzQw.png)

To test the 3D capabilities I've tried Kerbal Space Program and it works nicely, it's not stuttering and it runs pretty fast (I haven't tried complex ships). Only thing missing are the icons of the part categories. 

PC specs: 

* AMD Phenom(tm) II X4 955
* Gallium 0.4 on AMD BARTS (DRM 2.43.0, LLVM 3.8.0)
* Radeon HD6850

How should I proceed in attempting to fix this error?