Broke my Windows by activating a partition :(

hi guys, I was just trying out some stuff with the disc management, and I activated a partition that didn't have the OS, I don't think. So now when I boot up on that computer it says "bootmgr is missing". BIOs won't let me change the place it boots from either. I also tried putting Windows 7 on an external hard drive and booting from that. Can anyone help me? Also, I have a laptop with no CD drive, and I can get one, but I would prefer if there was a solution without having to buy one.

Download GParted (free) and boot on it. Remove the active flag from the partition you activated. That should fix it.

Thanks for the quick response.
So I can boot off it even if bootmgr from Windows is missing? Also would I have to format the external hard drive/flash drive I'm going to use?

GParted is just a partition editor/manager. It should help you undo what you did.

You will need to ensure the original system partition is marked active.

If you have a 100mb partition - that will be it.

If you don't, then it is either your main windows partition, or possibly the oem recovery partition ( if you have one )

Welcome to the forums, you could try booting from your installation dvd and carrying out a "startup repair" details from here:-
Startup Repair

Er, can someone teach me how to use it? I downloaded the one at Sourceforge, is that right?

Suggest you try the "startup repair".....

There is no startup repair, it loads up, then it says bootmgr is missing. And I have no CD drive.

Edit: And how can I make the makeboot.bat boot from an external hard drive?
Edit again: GParted says it only works on x86 machines, but I have 64x. Will it still work?

That would depend on you having a mobo that can boot from USB (check your BIOS) and it would probably be better to make a flash drive bootable and put your file on that.