[HELP ! ] Screen Resolution & Zorin Menu !!

Hi all !
i have installed zorin os 12 the last version and have this problem :
*The screen resolution is 640 x 480 and CAN NOT BE CHANGED !
here is the xrandr output :

Code:

xrandr
xrandr: Failed to get size of gamma for output default
Screen 0: minimum 640 x 480, current 640 x 480, maximum 640 x 480
default connected primary 640x480+0+0 0mm x 0mm
   640x480       73.00*


*the second is the zorin menu is not showing up when i click on the Z icon on the left ! How to fix this problems ! please i need help !

Have you tried changing boot parameters by adding 'nomodeset' by pressing E at boot time.

didn't work for me !
while i'am installing it , it was perfect graphic . But after it finished & rebooted , it become like that !
i found "unknown display" in the screen resolution part in settings .

OK, more information please:

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