Because of my stupidity i messed around with 'System' Volume Drive. I cleaned it and shrinked its size to increase size on my C Drive(Drive 'D:' was mentioned as 'System' in Disk management after a windows 10 install). Even after this i could use Windows for sometime. But when I restarted it showed the error "BOOTMGR missing press.....". So i tried to boot using windows 10 bootable USB, but I couldnt get into BIOS menu to change Boot order. Usually i Use F2 to enter BIOS Menu, but nothing worked. Im totally stuck, cant re install windows or flash BIOS. I can take out hard disk though, is there any way to flash bios from my other PC or Laptop?