windows not responding for bios trigger

[skj8501]

im using lenovo b490 laptop i messed up my windows c drive i deleted files through recovery i cmd,i cant boot now i tried with usb and all still not recogning the usb,i cant get to bios the triggers are not working and i was getting into bios by revovery option but now i couldnt
cause i deleted the drive c and changed the boot up setting to legacy only.i was using windows 8.1 and upraged to 10 and all messed up when i tried to revert to windows 8.1

 

[popatim]

If I remember right, to get into a Lenovo bios you have to interrupt startup by pressing enter when it says to and then pressing f2 (?) at the next screen. It should say which key to press to enter setup but I believe its F2. You may have the F2 option right after pressing the on button. Ours at work are older and wehave to use the enter key method.