Are you having trouble getting into Safeboot on the HTC One M8? Those guides that I used didn't help me because the way they told me to use the button combinations didn't work. The only button combination
htc one m8
HTC One M8 disable spell check and autocorrect
This works for all HTC One M8 variants like O2, VodaFone, T-Mobile etc.
In HTC One you go to the Settings – Language & Keyboard – HTC Sense Input screen and toggle off . Then move to Advanced