Can't change my screen resolution

[hazexm]

I have :
- a screen with 1366x768 resolution and a VGA port
- a GPU with HDMI port ( AMD HD 6670 1GB GDDR5 ).
i bought a VGA to HDMI adapter and it's working fine but i can't change the resolution to higher than 1280*768 although my screen supports 1366x768.
every time i change it to 1366x768 the screen goes black "out of range"
Note: it was running at 1366x768 when i was using DVI to VGA adapter but my GPU's DVI port is not working anymore.
how can i change the resolution back to 1366x768 because everything looks blury on low resolution ?

 

[i7Baby]

I'd use the cards VGA port with a vga cable to the monitor.

What make and model monitor?

 

[hazexm]

I'd use the cards VGA port with a vga cable to the monitor.

What make and model monitor?

my GPU doesn't have a VGA port that's why i am using a VGA to HDMI adapter i just want to know how to get the resolution back to 1366x768 ?
monitor model :ViewSonic va1931wa

 

[i7Baby]

According to http://www.amd.com/en-gb/products/graphics/desktop/6000/6670

It should have
DisplayPort 1.2
Max resolution: 2560x1600 per display
Multi-Stream Transport
21.6 Gbps bandwidth
High bit-rate audio
HDMI 1.4a with Stereoscopic 3D Frame Packing Format, Deep Color, xvYCC wide gamut support, and high bit-rate audio
Max resolution: 1920x1200
Dual-link DVI with HDCP
Max resolution: 2560x1600
VGA
Max resolution: 2048x1536