Windows Re install problems

So my dad has an old Asus laptop. He decided to fox it by using some guys advice of a forum. That advice was to right some code and apply it to windows. He has no experience with righting code -_- So now I'm charged with fixing it. We really need some windows iso file to repair it. Or my solution of just doing a fresh windows install. My question is that is there some LEGAL way to get a windows copy (for free) and then activate it with the windows key he has for the old laptop (LEGALLY). We have the windows key we just need the windows. Please dear god he has no idea what he's doing. 

Assuming his laptop is running 7 or earlier, in that case not really.  When 7 first launched there were sites that hosted iso's for digitally distributed versions and a while after but none of them seem to be active anymore (since 8 has been out most likely).  You could try and get a disk from Asus as installing from a vanilla iso will most likely not have all the drivers for the hardware in the laptop so it would be a pain downloading and installing all the missing drivers manually.

http://www.w7forums.com/threads/official-windows-7-sp1-iso-image-downloads.12325/

Tried it before I posted. All the microsoft servers are deactivated :(

Thats crazy. I just grabbed an iso a couple of weeks ago. I'll try and find the link but fairly certain it is the same one that is posted. 

http://www.heidoc.net/joomla/technology-science/microsoft/14-windows-7-direct-download-links

 

 

I was under the impression that if you had an activation key, the means in which you get an iso is irreverent..

With my understanding in mind, any torrent of the iso you need would be legal, so long as you use your key and not a activator.  If I'm wrong on this, swiftly correct me please.

Any iso should install, microsoft gives you something like 30 days to enter the key.