Maybe I got the solution. I installed Microsoft Silverlight so I could watch a tv serie. Silverlight was not compatible with Opera so I used Firefox. But after a while I discovered that Opera was so slow and even some pages didnt opened. I couldnt understand why but after a while I was thinking about Silverlight and uninstalled it, and yes now its no problem. Check if you got Microsoft Silverlight installed and try to remove it and restart computer and see whats happend.