OpenFirmware

I deleted my bootmgr from the command prompt window in Windowys 7 ( a mistake), and the next time i started my computer, a page came up saying that Windows failed tos tart because there was a hardware or soft ware change

File: \Boot\BCD

Status: 0xc0000034

info: The Windows Boot Configuration Data File is missing required information

Now, i tried inserting Windows 7 DVDs into the computer but the computer just refuses to boot from the DVD drive, so i figure the Boot sequence priority needs to be changed. I tried looking this up but it seems Apple has something called OpenFirmware instead of BIOS and i can't for the life of me figure out how to open this on startup. I've tried everything including windowskey+Alt+O+F , F1, F2, F8, F12, shift+10, c, and other key combinations people online seem to suggest, but i am jus not able to open it.

Please help me out

I'm willing to do a full overhaul/resetting to factory settings if need be..Just help me out of this

THank you