***POSSIBLE SPAM*** Trisquel 7.0 desktop problem

Hi Everybody,

I really would like to switch to GNU/Linux but i have some problems getting
Trisquel 7.0 working on my HTPC.
Yesterday I installed GeForce 8400 GS 512 MB video card in my HTPC computer.
the video card was detected by the OS without any problems
and is working fine.

I'm using a SAMSUNG 50" TV (HDMI) as my primary monitor (resolution
1920x1080, 60hz)
The resolution of 1920x1080 is automatically detected in the configuration
settings. (which is good)

But the problem is that the top (small grey menu bar) and lower bar of the
Trisquel desktop are not visible, so I cannot start any applications, etc.
(if I install Ubuntu 14.04 LTS on the same computer I don't have this
problem)
My SAMSUNG TV is detected as "SAM 7" on both Operating systems

What could be the case, that Trisquel 7.0 doesn't show my desktop good? is
there a easy solutions for this?