upgrade to 13.04 after log in black screen but f key opens screen shot and

[Uriah Heep]

Did on line upgrade to 13.04 after log only have black screen but if I hit
prtsc the window opens and by invoking error I get to Firefox. If i
minimize I have to hit prtsc again to get out of black screen and into fire
fox. Any suggestions to a novice on how to get my home screen back?
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