You can try the F10 key too.Which motherboard do you have?
Usually it's Del or F2 but can be F8 orF12 - spam those keys as soon as you turn the system on, and you should reach the BIOS.
Failing that, you might be able to reboot from inside Windows, straight to the BIOs. Hold Shift and select restart - keep holding shift until you're presented with the troubleshooting menu. One of the options (under advanced, I think) is to "reboot to UEFI".