[ubuntu] start-up - blank screen after login with working mouse

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http://ubuntuforums.org – HP Pavilion PV6700 - AMD 64x2 - 2G ram - Created live USB, got on and did a complete install. Now whenever I boot up it allows me to log on then goes to a blank screen and loads the mouse then just sits there. ctrl-alt-F2 works, and if I play around with the esc key I can sometimes get a blank desktop to come up where I can add a file then go into the file and then get to the file system. HELP :( the first few times is worked when I booted from the USB then it asked about a graphics update and after doing this the problem arrived... but it might have happened before I just booted from hard d (Hardware)