Q: My iMac (Mid-2011) Screen Goes Black

I had a little trouble recently with my 27" mid-2011 iMac getting green vertical bars on the grey loading screen, and took it in to my local Apple store for a repair. They initially said it was the LCD panel, but upon picking up the 'repaired' product, was told they had just replaced the video card.

Now, after getting it home (yesterday, May 16th), it took all of an hour before the screen starting going black. The music is still playing, and I can control it with my keyboard, so the actual system is running.

I've tried the usual (safe booting, PRAM reset) but all that happens is it'll sort itself out for a few minutes before going back to black.

My Applecare coverage literally ran out days after I took it in for service, and it's unlikely I'll be able to get it back to the store for a repair, which was one of the reasons I was so close to the end of my coverage when I did make it down.

Do Apple do UK home visits? And what are my options? Is my iMac still covered as this repair has not left me without problems?