This seems to be a problem in verification of your Xorg settings. Please you try to do the following:
1) before pressing "Yes" in dialog box, save your /etc/X11/xorg.conf file to some other place (and please post it here so we can check it)
2) after pressing "Yes", also save the 2nd copy of /etc/X11/xorg.conf to some other place (and also please post it here)
3) try to reboot - if your graphics is broken, restore /etc/X11/xorg.conf from 1st copy and reboot again (this should correct any wrong graphics changes made), so you won't need to reinstall
Also, what video card do you have?