Having left my surface pro in sleep mode and gone back to it several times, I have been able to either click the mouse or tap the cover to activate it. Hopefully this will allow me to use it without buying another one.

to whoever reads this, I have just discovered that my surface pro2 also has the same issue and the only way I can get it to startup is to hold both buttons and do a hard reboot. I am going to try and put my pro into sleep mode instead of switching off completely and see if I can overcome this problem. I can easily guess that taking it to BestBuy/ Currys uk that it would be too costly. I might have to do a trade in as the self fix option is not suitable or might not work even afterwards. Sorry I could not come up with a better answer.