Thanks for the reply,
It's a Sony Vaio. But that post makes sense, its got one of those 'AV Mode' buttons, which I think
may switch form onboard intel graphics to nvidia or ATI, so may well have the wrong driver listed in xorg.conf. I tried booting back up from the live disk, but when I look on the hard drive where Mint is installed in /etc/X11/ xorg.conf is not there at all
I also looked in the BIOS to see if you could set it to use only one of the graphics chips, but no luck.
I also tried to install Ubuntu, just to see if it would work, same problem, more or less. Just got a black screen instead of command line login screen.
Tried "nomodeset xforcevesa" too.
Any other ideas? Why cant I see the xorg.conf, can I just creat one? Feeling rather bad for borking his laptop presently!