GPU Problems

[HPTL7]

Hello.
I am currently playing Far Cry 3 on high settings with my Sapphire Radeon HD 4670 512mb Gddr3 and using dx11. No problems, lag. Nothing.

Now i bought a Sapphire Radeon HD 6670 1gb GDDR5. I went on Far Cry dx11 and ultra settings. It worked fine for a few minutes but then the screen just went blank.
So i powered of my computer by the power button and then went on Far cry and very high settings but same thing happened again.
I am currently using a vga screen. Im going to buy a hd screen soon.
Is it cause i am using a dvi to vga cable?

My spec:
Raijintek Themis Direct Contact CPU Cooler
Kingston HyperX 8GB (2x4GB) PC3-19200C11 2400MHz Dual Channel Kit - Black/Red
Gigabyte Z97P-D3 Intel Z97 (Socket 1150) DDR3 ATX Motherboard
Intel Pentium K Anniversary G3258 Socket LGA1150 Processor
Corsair 430w psu.
Sapphire Radeon HD 6670 1GB GDDR5

 

[mickyflinn]

Have you tried playing on lower settings ? If your going to upgrade to a 1080p monitor you will probably need a better gpu something like a 270.

 

[HPTL7]

I tried using DX 9 which worked perfectly with my other GPU and same thing happened.
Also, won't this GPU be fine on 1080p screen? It has HDMI input and I don't mind playing games on medium settings

 

[HPTL7]

I have another problem now. My Pc won't start. I press the power button, the led light comes on but nothing starts except for the PSU. Nothing else, no fans nothing.
Is this the GPU fault?