I have Lenovo y480 with Ubuntu installed on it. I installed Ubuntu from a bootable usb. Also, My computer was able to boot into live Ubuntu on usb fine. Today my laptop stopped recognizing any kind of bootable usb. No matter what bootable usb I plug in, bios boot menu just shows optical disk, hard disk and network boot options. Another thing is Bios stoped saving any changes to settings/configurations. If I enable or disable some setting and then save it , when I restart those changes are gone. Also, if I boot into Ubuntu the usb gets mounted automatically and I can see the contents fine. How do I get my laptop to recognize bootable usb again?