Help!

Not a Henry type of Help, but 'please help I'm a bit stuck'.

All of a sudden, the display on my PC has gone a bit haywire. Everything functions, but some images, well, just don't display right. It's most noticeable in web browsers... any web browser, but seems to be the case outside of it as well.

The problem:-

• Graphics look "blocky" - for example, the Google logo has definite lines of transition between one shade of blue/yellow/red to the next, rather than a smooth flow.
• Lines lack definition. for example, PVP is pixellated, rather than fluid pen strokes.

And more but you get the general gist. It's almost as if I am running with too few colours. But I'm not - settings are set to true color.

Attempts to correct this include:-

• Changing the display properties
• Upgrading the graphics card display driver
• Rebooting (always worth a shot)
• Checking all connections

Any ideas?