I have a ThinkPad T430s and after messing up with partition flags I'm no longer able to access any of my OSs. When I boot the computer it goes straight to Windows 8 and i get the 0xc0000001 error. At this point I would just like to enter the BIOS to change the boot order and reainstall the OS but whatever I do on the ThinkPad start screen I can't access the BIOS (I used to only need to press enter, now I tried every combination that anyone ever suggested on the internet to no avail). Is there any way to either access the BIOS in some alternative way, or to input some kind of command on startup to make the PC boot from the optical drive?