Heisenbug was coined by much-missed Jim Grey, of Fourth Paradigm fame; even better is his companion term for plain ordinary easy to find issues - Bohrbug. Be my hero and add the attribution.

ok, pressing the Windows key down BEFORE hitting power is the key ;-) and if you don't want to plug in a keyboard, on the Save & Exit page of the BIOS, volume down to get to P0: SAMSUNG MZMPA128HMFU-00000 at the bottom and rotate button enter to select that made my slate boot from the USB stick straight away...

Sooo ;-) I did the upgrade install from 7 but I'm having a few problems (the Windows key stopped working after I tried to see if the Samsung drivers would give me rotation and rotation lock & even the new rotation driver hasn't put it back - if I double tap it I get the switching pane thumbnails, but just pressing it does nothing - and I have no option to turn Bluetooth/wifi on and off independantly, just airplane mode, plus I want to junk the recovery partition for space) so I thought I'd do a clean install. But because the Windows button doesn't work, I can't get into BIOS to turn on USB boot... Does anyone know an alternate way of opening the BIOS if I plug in a USB keyboard? Or a way of putting the Windows key back the way it should be?