Since installing Windows 10 the option to enter BIOS settings disappeared on my HP Pavillion DV8, with the only way to get it back was to pull the CMOS battery from the laptop and perform a hard reset.
If you’re having the same trouble the solution is easy, instead of clicking shut down to turn off the laptop and switch it on again, click restart instead! Seems simple but I always used shut down to allow the machine to cool off before turning on again.