Just tell them what it looks like if you're discussing it over the phone.
They have better diagnostic tools and procedures than you to figure out the cause of the failure anyhow, it's rather pointless to try to determine the cause yourself. A detailed analysis requires physical access to the object in question anyhow.
One thing: you may wish to get a second price quote from an independent computer repair shop (one that is an Apple authorized service center, of course). Apple Store repairs are not cheap.
Good luck.