Just thought I would share my experiences of this particular type of problem so that others might be able to properly get their iBooks fixed should this problem arise. Basically the symptoms are as follows Boot up machine, cd rom drive makes a noise or two as it does in a normal boot process, screen flashes itself so that its "on" though doesnt display anything, finally the system fan kicks in, on high speed (in normal operation I have never heard it at high speed, this is the one time when I have really heard the fan, and I do mean really heard it. Think original GeForceFX card.) That is about all the machine will do. You cant boot into single user, target disk mode or anything like that because it just never gets that far. If you get this symptoms then I recommend checking your warranty information and then calling Apple support, they will probably get you to perform a few key combinations during the boot process, most of which will fail. At this point I was then given a case number and informed of my nearest Apple Authorised Retailer. From there you take the machine to the retailer and they will replace the logic board for you, time for this will vary depending on the size of your apple retailer, smaller ones will likely not keep the board in stock so you will have to wait longer, larger ones which can keep a supply of parts the wait should be much shorter. I do hope that this information helps people who experience this problem. To be perfectly honest I was incredibly pleased with the conduct of Apple support and shocked that there was even an Apple retailer so close (5 minutes walk) but as with all things the "mileage" may vary on the latter.