Exact Same thing happened to me, went into the apple store after the black screen and what not. They did the test and it turns out its the logic board IS dead, long story short, they told me tough cookies, its gonna cost 700 for the new logic board and 200 for labour. I had my computer for a year and a frackin half, 1500$ computers should last longer than a year and a fracken half! All in all, at the end of the day I buy a new macbook, lowest end model. A new computer costs almost the same as replacing a logic board what a load!
*This were I have a question though a few weeks later, I take out my mac pro and decide to try turning it on again, and it started up, the screen came on, it worked all afternoon, I moved all my files onto my external harddrive. but after my computer went to sleep that night it wouldn't start... again.
So whats the deal, is it really the logic board that failed? Because it did start up after they diagnosed it as logic board failure. Maybe its just a loose wire, or maybe it just needs a cleaning? I dont know, can anyone help?