Accidentally marked drive C as active

I started O&O partition manager and accidentally pressed active on partition C and now I cannot boot windows...

I am using build 7600 x86 I loaded up the windows 7 iso on a usb memory and booted from it and chose repair, it said it found things to repair, i pressed ok, it rebooted but it did not help, now I chose from the repair menu to automatically search and fix, it said startup repair cannot repair this computer automatically and it want to send information about this problem, I wonder how it figured on doing that...

oh yes i started the repair again and pressed command promt and followed this guide: MBR - Restore Windows 7 Master Boot Record and the first thing it said about D being the "DVD" was wrong in my case, it was E and from then on the guide was excally like in my case and I completed the guide, rebooted and still the same message "BOOTMGR is missing Press ctrl alt del to restart"

So what can i do to fix this? without needing to reinstall windows

If you can reach the Recovery environment thru usb, open command prompt and type:
C: (Press Enter)
diskmgmt.msc (Press Enter)
See if you can open disk management, if yes, revert the changes that you made.

when you open command prompt, by default, it will stay on X:
You'll need to come to C drive and then type diskmgmt.msc

Or, on the C:\ prompt,
type the following commands and press enter.
diskpart
list volume
select partition C
inactive

Reboot your computer.

now type select partition X (where x is the partition you marked active)
then type inactive
Restart your pc.

sad to hear that.