Having just bought a new IMAC, I was not in a good mood when I had some problems with the machine. First, bad pixels (fixed by a different shop), second (and far worse) the machine kept locking. I bought the MAC to avoid this problem! After a few calls with Apple, they put me in touch with Techsuperpowers. They came out to my house from Newbury Street, tore down the computer, but the equivalent of a motherboard in, and ran all kinds of tests to make sure none of my memory chips or other "things" were causing any problems. They did a great job, as my computer runs like a dream now (as was hoped). Their rep was timely, and did a great job.