OK try this. Go to system settings, and monitors. If 1024x768 is not in the list then you will have to add it. First choose your monitor, or if you don't know exactly which one to use then go with 48KHz because that should give you 1024x768x60hz. Then add a mode, and pick 1024x768 from the drop-down list. Save the settings and reboot.
Now go to system settings and screens. Click on Ambient, and then edit, and choose the 1024x768.
