BOOTMGR missing, bootrec.exe access denied

Hey, recently, a friend of mine deleted something that he shouldnt have (or did something he shouldn;t have) and now, BOOTMGR missing keeps coming up, i've been trying to fix it for 2-3 days now and well, my current situation is that i cannot boot any CD from my disk drive, I have windows 7 Ultimate disk, i have windows PE iso, i can boot via USB.
So, i got the winPE into the pendrive, and it worked, now i got into it, and ran startup repair, and it said that the problem cannot be fixed automatically. I opened up command prompt, and put in "bootrec.exe /FixBoot" and it came access denied, i have no idea what to do now, and couldn't find any conclusive answers from other posts that i saw.
I don't mind re-installing the whole Windows 7, but i have important information there, and my present resources are a rewritable DVD, and 1 GB pendrive (not enough to store all of it). So, i could really use some help now, please.

Thanks for replying so soon Tews, yes i know i could have completely avoided this, and i was foolish to not backup, but as i mentioned, i cannot do the above mentioned procedure, I have a lot of data and not enough space to cover it. Is there some way that I can just reinstall, and all files that i specify will be unchanged?
Or is there some completely different way all together?

I shall try that as soon as i can, thank you.

Okay, got a few more problems For some reason my DVD doesn't boot up at all, but my usb does, as i am using a live USB linux atm, and so i followed some guides, put the DVD data onto a pendrive, and then booted it up. Now it started, but i couldnt do an upgrade, and when i tried to custom install, it came check the source, and never went further. I do not have any other dvd drives on the laptop, and so i tried out an external DVD drive, but hen i put boot from USB (as it was connected to usb), BOOTMGR missing came again. Now what can i do??