Blacks are horribly grey and washed out.

I've done much googling on this matter but can't find a decisive fix.

Graphics card is an Radeon HD 5450 and it's an HDMI connection from PC to panel.

Am running XBMC so i don't want any change to adversly affect that (don't want much do i?!), as black levels are spot on.

Any learned users who have sorted this please?