I login in Ubuntu and just appears the mouse cursor

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http://askubuntu.com – I try to install Ubuntu in a VirtualBox (in Windows). It works perfectly. After that, I try to install on the physical machine. When setup ask if I want to "try" or "install", if i choose "try", I get faced with a wallpaper and a mouse cursor but thats it. Nothing else happens after that. No desktop, no icons, nothing but the wallpaper and mouse cursor. If I install happens. What's the problem? I have a 1.80GHz processor, 2GB RAM, 500GB HD, MSI - R5450-MD1GD3H/LP (1024MB). (HowTos)