Hello, 

I recently bought a PowerColor Radeon HD 6790 to replace my old gpu (AFOX Geforce GTX 550 Ti).
It came with a DVI-A to VGA adapter, a CD-ROm and a 'Quick Installation Guide.' So I uninstalled the old card and took it out, put HD 6790 in and used the CD-ROM to install the initial drivers then later updated it.

I used the DVI-A to VGA adapter because my monitor only has a VGA input. When I did, the screen keeps turning on and off irregularly and renders the computer rather unusable. 

Thinking that the DVI-A to VGA adaper was at fault, I bought a new DVI-I to VGA adapter and the same result occurs. 

I then tried to take advantage of the HD 6790's Mini DisplayPort, so I bought a Mini DisplayPort to VGA adapter; which worked fine, until I play a 3D game (SimCity 2013), in which the screen switches from black to normal in rapid succession and you can hear the sound which Windows plays when you remove and insert a device.

I moved my PC to the living room where there was a HDTV with an HDMI input. I used an HDMI to HDMI cable, but the same problem occurs as with the Mini DisplayPort to VGA. Even with the DVI-I to VGA and DVI-A to VGA adapters (the HDTV has a VGA input as well), the same problem occurs too.

Frustrated, I took the HD 6790 out and replaced it with my old card (AFOX GeForce GTX 550 Ti). Everything works well. Since GTX 550 Ti had a DVI-I output, I tried to use the DVI-A to VGA adapter that originally came with the HD 6790, and it works well, no problems encountered.

Am I to assume the GPU unit I obtained was defective and I should return it?

My PC:

Graphics Card:

PowerColor Radeon HD 6790

AMD Catalyst Driver Version, and Driver History

13.1

Operating System

Windows 7 Ultimate 64-bit

Motherboard:

ECS A880GM-A3

Power Supply:

Vision 600w Power Supply Unit

Display Device and Connection Used

ColorView 15.6" LED Monitor Model No. E1608

VGA male to VGA male (came with monitor)

DVI-A to VGA Adapter (came with PowerColor Radeon HD 6790)

DVI-I to VGA Adapter (store bought)

Mini DisplayPort to VGA Adapter (store bought)

HDMI to HDMI cable (store bought)

Applications and Games

Windows

SimCity

CPU Details

AMD Athlon II X2 260

Sytem Memory Type and Amount

Kingston 4 Gb DDR3

Additional Hardware:

1 Samsung DVD-RW

4 120 mm fans

1 500 Gb HDD

Additional Details

Clean Reformat

Thank you for any help!