Hello. A friend of mine have a pc with invalid windows 7 installtion (I get a message that that I may be a victim and so on...).
I have a real original windows 7 pro copy that is still new and wasn't registered yet.
Can I register the bad copy with the key of the good one so it will be legal and she want need to reinstall windows 7 (because then she will need to install all the other programs she already install on it).
I'd research how to change the Win7 product key instead of do a new install. I had a procedure for WinXP but it won't work in Win7. You should also be able to call Microsoft and have them help you activate over the phone.
In case of different version (Home Premium vs. Professional vs. Ultimate and Retail vs. upgrade vs. OEM), the answer is definately NO.
In case it's same version, then there is a way to change the key, although I don't know it (never used it). But it's not a guarantee that it works.
To sum it up, it's a small chance that it would work. So be prepared for the worst case.
1) click on start
2) right click on computer and click on properties
3) this will open a system window at the bottom is windows activation click on Change Product Key
4) type in new key, should be good to go after that
I would suggest a clean install, however if they are the same "bit" you should be able install it over the invalid one by inserting the disk while logged into windows. This works like Upgrading from Vista to 7 version won't matter, and all the programs and files should still be there.