Funny how Brits are so reluctant to RTFM - including me!
Had the same problem. Tapped the <ENTER> key as per the manual - no go. Didn't want to use the hard reset button. Wondered about the battery. Plugged it in for five minutes and tried again. Tapping the <ENTER> key worked this time and battery showed 100%. Can't be sure what the problem is but concluded that either the unit got too cold overnight or the power-handling soft/firm-ware is imperfect and sometimes needs a kick, eg plug in for a few minutes. The latter wouldn't be a big surprise - it comes up regularly on Linux fora for the big brother laptops. Laptops of any ilk with Linux are an extremely new innovation - plenty of examples of auto-cooling failures, sometimes leading to very expensive damage; another reason to use a low power, fanless machine.