i tried installing ubuntu on previously windows 8 machine. On operating system i choose ubuntu and it won't load and i cannot choose windows 8. I tried to switch back to win 8 before my 10 seconds run out but it seems it doesnot take my keyboard input.

It says windows boot manager and on next screen it says windows failed to start.
 It says insert installation disk and restart n repair.

it gives some error status code as 0xc000007b.

it says required file missing or currupt
 
\ubuntu\winboor\wubildr.mbr

now i am not able to do anything and i don't have any win 8 installation disk. Please help.