kiymara

When I log onto SL I cannot see my avatar just a white oval not a cloud an oval like when your messing with the paint program on windows, everybody else can see me but I can't. And some of the other people appear as white oval's as well not all of the people just a few. What can I do? I already uninstalled it and reinstalled SL I tried both firefox and internet explorer, It was working fine yesterday now its not what should I do.