Dell precision t7500 - constant beep when installing two different GPU's

Hi Can anyone help me!?

I am trying to install tow different GPUs in my T7500 Option 1. for my gaming and Option 2. for my CAD/rendering as follows:

1. Primary GPU -= AMD Radeon Sapphire R9 280x vapour 3gb

2. Secondary GPU -  ATI v9800 firepro 4gb - 

However, When I try to install the second GPU in the second slot it constantly beeps even though I have connected the power cables to this second GPU?

Please can anyone advise what to set the bios for having to GPU's i.e. option 1 or option 2?

Set up as below for my primary GPU..

Graphics Card Manufacturer - Powered by AMD
Graphics Chipset - AMD Radeon R9 200 Series
Device ID - 6798
Vendor ID - 1002
SubSystem ID - 3001
SubSystem Vendor ID - 174B
Revision ID - 00
Bus Type - PCI Express 3.0
Current Bus Settings - PCI Express 2.0 x16
BIOS Version - 015.040.000.001
BIOS Part Number - 113-2104XTLAFR-U42
BIOS Date - 2013/10/18 01:40
Memory Size - 3072 MB
Memory Type - GDDR5
Memory Clock - 1550 MHz
Core Clock - 1070 MHz
Total Memory Bandwidth - 297 GByte/s
2D Driver File Path - /REGISTRY/MACHINE/SYSTEM/ControlSet001/Control/Class/{4d36e968-e325-11ce-bfc1-08002be10318}/0000

Thaks

Paul