I bought a Sapphire HD 7950, and tried to install it. Upon booting up it would beep 6 times then the power light would just stay on. I did replace the power supply from a 300w to a 550w prior to putting in the new card. Originally the computer was a rebuilt HP Envy H8-1414 with the power supply being the only thing I've changed.
Here is a link to the full specs of the HP
http://goo.gl/3dwRgy
Here is a link to the full specs of the HP
http://goo.gl/3dwRgy