Hi. I recently took my imac to the apple store to have it repaired. They told me that I had a bad Power/Audio/Video Board and that it would cost around $300 to fix. I took it home and found a PAV board for $50. Now I originally bought this at a yard sale, it worked so I upgraded to os xv10.2 not knowing that I needed to update firmware. After that it worked for about a day then the monitor quit. I replaced the PAV and turned it on. Now when I turn it on the only thing I have is a blue screen. What do I need to do now? Thanks.