I have just upgraded my graphic card to a Radeon HD 6790 CoolSteam. The card says its compatible with PCIe x16 which i have, minimum of 500w PSU i have 550w, min 1gb memory i have 4.
It still wont work though, I am putting it into an Asus p5n-e sli motherboard and have updated the bios to the latest version and still it wont work. The pc boots though as you can here the windows start up sound through the speakers.
Do you have your external power connector firmly attached to the new video card? Also, is both your 4-pin and 24-pin power supply connectors firmly inserted into your motherboard? Last, what video card were you using before adding the HD6790?
Does anything ever get displayed on the screen (like the BIOS splash screen)? BTW, the fan would turn on the video card even if the external power connector was not in place due to power drawn from the PCI-E bus itself.
There is no splash screen monitor displays 'no signal check video connection'.
With regards your fan comment that may be an error then as if the power lead is not connected to the card the fan does not spin.
The power supply i am using is the HEC 550TD-PTE (550w)
Understood on the PSU make/model. I am not a fan of that brand due to quality issues I have seen in the past.
This could be the issue here. If the power supply isn't providing adequate power the system, then the GPU is going to be negatively affected.
How old is your power supply? Also, you really can't go by the power rating on some PSUs and older power supplies are less efficient/effective than newer ones. They do wear out.
Regarding supplying power to the video card. Power comes from 2 sources, the motherboard slot and the external power supply. Typically, when you fail to connect external power to a GPU that requires it, a warning is displayed when you first boot the system. In that case, there is enough power provided via the motherboard to allow this to happen.
In your case, I suspect that the video card itself is defective. If you can check out in another system, then I recommend doing so. Also, do you have the option to return/exchange it?