After i wrote the window key it gives me a msg it invalid key while im that its correct one which is written on the pc so what can i do to activate the window after reparing

Make extra sure that you have typed in the correct number.
It may be because the serial has been used before on a different machine, or you have exceeded the maximum number of installations.
Your best bet is to contact microsoft technical support in a situation like this. I am sure that they would be happy to help.

You can try using the "Magical Jellybean Keyfinder" (http://www.magicaljellybean.com/keyfinder/) and see if the key installed on your machine is different than the one that is on the PC.

If this key doesn't work, you may be a bit stuck. You may have to call Microsoft and have them issue you a new key for the activation. Generally, they are pretty nice about this, as long as your copy of Windows is genuine.