1) Believe the continuous beeping you hear is a BIOS Beep Code, stating you have a graphics problem. Computer, not video card, is beeping.
2) Do you have the external 6-pin PCI-Express power cable plugged into the graphics card, from the Power Supply?
3) IF, your Power Supply does not have a 6-pin PCI-Express power cable, are you using TWO 4-pin Peripheral power cables, connected to a 6-pin PCI-Express adapter power cable?
6-pin PCI-Express power cable example, and also showing a 6-pin PCI-Express adapter power cable on the right,http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress
Example of a 4-pin Peripheral power cable,
(Misnomered by many as a 'Molex' power cable. Molex was the first company to make that type of connector. The name stuck, kind of like calling an adjustable open-end wrench a Crescent wrench),http://www.playtool.com/pages/psuconnectors/connectors.html#peripheral
Note the color code of the wires used in a 4-pin Peripheral power cable, and a 6-pin PCI-Express power cable.
Red = 5 Volt wire
Yellow = 12 Volt wire
(All are DC Voltage)
Black = Ground wire. (ALL Black wires are Ground wires)
The 4-pin Peripheral power cable has ONE Yellow 12 Volt wire.
The 6-pin PCI-Express power cable has TWO Yellow 12 Volt wires.
The most power that a PCI-Express x16 expansion slot can deliver, is 75 Watts.http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress
"This cable is used to provide extra 12 volt power to PCI Express expansion
cards. PCI Express motherboard slots can provide a maximum of 75 watts."http://www.playtool.com/pages/psuconnectors/connectors.html#pciexpress8
"The older 6 pin version officially provides a maximum of 75 watts
(although unofficially it can usually provide much more)"
The ATI FirePro V7800 graphics card requires 150 Watts by itself.
The PCI-Express x16 expansion slot CANNOT deliver the recommended power (Wattage) needed, therefore an external power cable capable of delivering 75 Watts is needed.
What happens if you just use ONE 4-pin Peripheral power cable, in a 6-pin PCI-Express adapter power cable?
The PCI-Express x16 expansion slot contact pins -> BURN
The gold plated contact pins on the bottom of the graphics card -
The connection on the graphics card for the 6-pin PCI-Express power cable - BURNS
The contact pins in the 6-pin PCI-Express adapter power cable -
If it is too bad, and cannot be remedied by cleaning, the motherboard is TOAST, and so is the graphics card.
For additional questions please post in a Comment.