I have an appointment to take my Mac in to the Apple store on Wednesday. This is my diagnosis, and I hope it is what they find too and can fix quickly: http://www.apple.com/uk/support/imac/powersupply/repairextension/
Not sure if it matters that it is the UK.
BIG challenge here- what I'm going to do for working on a machine while mine is in the hospital. I'm going to try to beg for the floater mac at Luxottica. Basically they are my only client right now anyway, so morally, it doesn't seem wrong. If not that, I'll be working on Greg's laptop at night and will have to restructure my days. And we're seeing what we can do to juice up our mac at home. Greg has helped me greatly in keeping my head with this.
I knew this day would come, but what can you do? I can't afford ONE mac, let alone TWO machines for a backup. My plan has always been to get a laptop in the future, but profits just don't allow it yet.