I thought that my ATI driver was not running well so I wanted to re-instal it completely. I did:

sudo apt-get remove --purge fglrx*
sudo apt-get remove --purge xserver-xorg-video-ati xserver-xorg-video-radeon

and after a boot I wanted to intal the ATI driver BUT at the boot no more signal to my screen.

Since, every time I turn on my PC it gets to purple screen and then screen shuts down !

Note that:

• Even if the screen is off, PC seems to be running almost well: I m still able to use my network to access data shared with NFS.
• Using live USB I have no screen problem.
• I tried to plug my screen on an alternative output but it did not work.
• I tried CTRL+ALT+F1 while being on purple screen but it does not do anything, screen shut down anyway.
• I m going to try the SHIFT thing and learn from blackscreen wiki...