Asus P8Z77-V LX wont let me OC

I have an intel 3570k and an asus p877-v lx and im following this guide to OC: http://www.overclock.net/t/1323214/overclocking-i5-3570k-using-asus-p8z77-v-lx (scroll down a bit) I've followed this so many times but today when I try OC i get to the final step and when i type in the CPU ratio (as 40) and press enter it automatically resets it to 34 and turns turbo mode off, why is it doing this? I recently installed an Evo 212 cooler today too, could that be anything to do with it? Again, ive done it so many times but i reset the BIOS and installed a new CPU fan today and now it won't let me OC and keeps resetting the ration whenever i press enter