Kubuntu 12.10 on a new PC, has been working fine.

Just had a power cut, and on restarting I see the BIOS on my screen then it goes grey and stays that way. I can tell it's booting up (combination of HDD lights etc, and the fact that if I wait long enough I can SSH in to it). But nothing on the screen.

It's possible, but no means certain, that I had does some apt-get upgrade's (or dist-upgrade's) prior to the power cut that have now come into effect,

How do I debug this to get my desktop back (by which I mean visible to me - I'm sure it's there!)?

In case it helps:

$ lspci | grep VGA 00:01.0 VGA compatible controller: Advanced Micro Devices [AMD] nee ATI BeaverCreek [Radeon HD 6530D]

It's just a default install, no graphics tweaking (I haven't even installed proprietary drivers). Monitor is Edge EF220A (1920 x 1080).

Mark