Can't access bios on Lenovo thinkpad s431?

Hey guys interesting problem here… I'm trying to access the bios menu on my thinkpad s431 laptop and I do this by pressing the function buttons at the splash screen but that doesn't work. The computer just zooms pass the screen not giving any options for pressing. I updated the bios and that worked once, It gave me the option to interrupt the startup by pressing the enter button. But now that option is gone and I can't get it back. For some reason though I pressed all the buttons a lot of times and that also worked once and got me the enter option but now it's gone again. I've tried pressing all the buttons but its not working anymore.