Windows 7: 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.

i got to the stage where i entered diskmgmt.msc and it said that it was not recognized as an internal or external command bla bla...

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

i typed dir and it seems to be my C: drive, does how do i enter the 100mb partition? where i can 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.

i typed in diskpart and this is what it says:

actually I´m gonna include a picture, that should explain more clearly.

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

yeah i did that, then rebooted and it booted direcly from the usb memory, i disconnected it and now there wasn´t even a bootmgr error anymore, thanks anyway, I screwed the pooch on this one, Reinstall...

sad to hear that.