The problem might be;
1. The resolution is not compatible with your monitor
2. The Resolution is a poor choice for your graphics card (I doubt 1 and this)
3. The resolution might not be compatible with RA2
4. Your GUI was installed wrong and as a result, KABLOOEY.
But I'm not a doctor.
I can see right now that I am going to have to set a post limit for new guys to post in Technical Support ..... IF YOU DON'T KNOW, THEN KEEP OUT!!!!!!
Now, to help.
Go in your game folder (which is usually C:\Program Files\Infrogrames\Robot Arena 2) and find ra2 and open with notepad
Find
FSDisplayWidth=800
FSDisplayHeight=600
FS3DDisplayWidth=800
FS3DDisplayHeight=600
and change to your resolution.
If you have an nVidia vidoe card, you may need to 1.3 patch your game.