installing new theme

Hi there, I am having a problem whenever i try to install a theme from the selection provided. These are the steps i follow.
1.Click on appearance
2.click on themes
3.click on install themes
4.click on find themes
5.I then preview and select the theme that i like
6.click on install
Whenever i click on install a blank white box comes up with the top right hand of the box saying: install “name of theme” and nothing else happens.However when i go to the “manage themes” screen i am able to activate any of three that is there,but i would like to use one from the vast selection that is available. Please help. Thanks