Problem solved - got an old laptop up and running which seemed to be having no problems, so I figured it must be something in my PC. Began uninstalling programs that I'd installed around when the problem started and it was this stupid bit of software to update my daughters V-Tech toy! Gaming is now fun again.

It feels like popping a particularly troubles zit. Very satisfying...

I'd never have done it without Pingman and his super powers!