I've got a 2 year old MacBook Black. It's been fine up till a couple of weeks ago, but I've had a succession of problems with it. The only thing I've changed recently was the memory (I upgraded it to 2GB, to make it run faster with parallels), which I bought from Crucial.com, rather than Apple. So one day it wouldn't boot up into Windows or OS/X. I ended up erasing the lot and reinstalling. Disk Utility found an 'invalid node structure' error. I erased and rebuilt it... seemed fine... then one day it wouldn't boot up. I erased and rebuilt it again... it took several attempts. It's also had periods of running very slowly, intermittently. The latest problem is it's not booting up. Disk Utility on the Leopard Disk says it's got 'Invalid B-Tree Node Size'. I can't read the disk (in fact it doesn't even register in Finder) when I boot up the machine as a fire-wire drive, using my other machine (MBP) connected to it. So there's a problem here that the rebuild hasn't fixed. I'm guessing that the hard drive is on the way out, and the succession of issues I've had is down to that. I've just swapped the memory back to the original, and I've still got the same problem. So, before I buy a new hard drive, is there anything else you'd suggest?