This is exactly the same as my 360. If I turn it off then back on it starts fine and I've had no problems in games. I've tried starting with or without a game or setting it to go straight to the dashboard but it makes no difference. It's sometimes ok if I only leave it off for a couple of hours. Same starting from the controller too.

When it doesn't boot the fans seem to be running but not as loud as a normal boot and the green quadrants do not do the pattern.

Mine was bought the end of November 07 but was a Christmas present so hasn't had much gameplay and it's usually only on for a couple of hours at a time.

I think I'll stick with it for now as I've heard people have sent them back and had worse ones sent back or had to wait weeks and I've still got quite a lot of warranty left.

Be good to hear if anyone finds out what's happening.