Buddy, Send it back - Whenever I have had a mac which didn't work properly I have sent it back (one so far thankfully) and then refused to have it back untill it works.
My friend did this and gave me the advice.
Generally they will play with it a bit more rather than screwing around with a diagnostic tool and then they realise like we do "oh this machine is shit - there's something wrong" and then they fix it.
I have just had this happen on my mac mini - I sent it back, they rang me saying they couldn't find anything wrong, so I said check the log (then thay thought "ooh he knows something", then they went away for two weeks, then rang me saying they have replaced it.
My default postion with mac, and I have had 6 machines so far, is that they all work perfectly, so when one doesn't, I'm complaining, I am not a techie, so I'm not going to fart around with Unix, but I can dial TNT and pay for postage.
Hope this helps