i have found pressing 'CTRL + ALT + DELETE' and click 'TASK MANAGER', then click in the processes tab at the top (the second tab in), then click on 'explorer.exe' and click delete. It will come up with 'Are you sure' or similar, click yes. Then click on 'File - Start New Process' A box appears then type in 'explorer.exe' and hit enter.
Explorer then starts properly and all will boot correctly as it should.
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Life is too serious to be taken seriously 
Copy/pasted from http://en.kioskea.net/forum/affich-56124-windows-7-black-screen-issue
Message was edited by: rich912