Hi Abidmoncef,
Thank you for visiting the HP Support Forums and Welcome. I have read your thread on your HP Pavilion dv7-2005el Notebook and getting a blank or black screen on watching a video. Try performing a hard reset. When performing a hard reset please note remove any and all USB devices, and remove memory cards from the card reader slot. Disconnect all non-essential devices. Here is a fix from Microsoft. If that does not help try to turn on the computer you start to press F11 repeatedly till the menu opens. You can do a system restore. System restore would restore the computer to before the error started. You could also check the hardware to make sure all is well.
Hope this is helpful.
Thanks.