Unplug the power cord from the wall socket and remove the battery. Press and hold the power button for 20 seconds. Now return the battery and plug the laptop back in.
When you now boot up, pressing the BIOS access key should work.
The reason is that killing all power and draining any residual should take the laptop out of the hybrid sleep mode it is stuck in, so it can do a real cold start.
1) Boot to the Windows 8 login screen.
2) While holding the Shift key, restart the computer.
3) Click on the Troubleshoot button.
4) Enter UEFI Firmware settings.
Please try to abort booting three times in a row by holding power button pressed when you see rotating dots. Recovery environment will have an option to enter UEFI settings.