thanks serv,
my ubuntu is normal gnome , but last night someone advised me to enter recovery mode while booting ubuntu because it was shown to me every time i start ubuntu to choose what mode , it took a bit of time & then i restarted again , i dont know exactly what happened , but after that ,my ubuntu works excellent now , i tested it a lot of times ( shutdown & startups) , visual effects , drop shadows , & all compiz features & parallels tools are working great now .
again thanks serv & Parallels.