HDMI setup problem

Hi,

I have an Ati Radeon HD 5770 video card, with HDMI and DVI outputs.
For the moment, my monitor ( Asus MS228H ) is linked to the video card with VGA cables; monitor has also a VGA out and for the video card i use DVI to VGA adaptor.
Since my video card and monitor, are both capable of HDMI and have hdmi outputs, I want to try this method, as it has better resolution, details, etc.
When i switch to HDMI cable, there are some problems:
-the entire image is framed with 2 cm black edge
-all the text is  blurred
What step in HDMI setup am I missing?

Thanks