Help! cannot boot from cdrom/usb/got error msg ‘bootmgr is corrupted

Hey guys, i need help with aspire 4736z. The problem is the windows is corrupted and when i try to boot using cdrom/usb it doesnt detect and i had my bios settings correct with the priority boot set up. And when am using external cdrom i get bootmgr is corrupted error msg..what can i do?do i need to flash new bios?