You can go in to bios, under exit menu, reset bios to default settings. Save and reset see if that changes anything.That was my next point of call to do tonight - i've been very conscious not to overtighten the screws when fitting the cooler as instructed on the Manual. Annoying i will have to take off but oh well! After this step and putting everything back to stock and if it's still not working - is there anything further you would recommend? (ie looking at Bios etc?)
Everything in my opinion was fitted fine (the liquid cpu is a recommended upgrade for the HP Omen