Problem with a 4850 x2

[MAURO]

I purchase 4850 x2 but after the installation of the latter my PC does not last I want to say there is no boot window, there is a l 'screen, leaving just my 8800 no problem just starts normally. It can not SAGIR a supply problem, I just change it at the same time as the card is a power supply 700 w.
I restart my system with my 8800 to install the ati drivers, reinstall the 4850 x2 but not work anyone help me ?

[Bradan]

What was the PSU ? The card is powered by the PCI-E? The card is supplied with two 6pin connectors?

[MAURO]

The PSU is a Hyperion power 80% + and the fan is a 14 mm power supply does not come from street trade, but only CG I misspoke in my first post.
And yes GC is connected with 2 PCI slots a 6 pins and 8 pins.

[EDRIC]

logically a tower can start if there's no graphics card, there's nothing on the screen but there's no need for a graphic card work.