have you tried to press Alt+F10 keys at boot too?
try also to enter BIOS and check if F12 boot menu is enabled, so you can press F12 key at boot and then choose your USB flash media.
have you tried to press Alt+F10 keys at boot too?
try also to enter BIOS and check if F12 boot menu is enabled, so you can press F12 key at boot and then choose your USB flash media.