actually this is a new laptop with an installed OS but then after a few months I can't activate this key. I think I have a corrupted files or something
The thing you 'clicked wrong' was downloading that pirated version in the first place. The second thing you did wrong was trying to install it.
Buy a new, legal, valid copy of Windows, from a reputable retailer or Microsoft.
Install with that, wiping the entire drive.
After that, if you really need an office suite - either pay the money for MS Office, or use one of the free, open source alternatives. LibreOffice or OpenOffice.
yes yes.. That's what I plan but it'll cost a lot =_=.. My anti virus has expired so I should buy one. Anyways, do you have any suggestion for a good antivirus. The installed anti virus was McAfee but I plan to buy Kaspersky. Any suggestion?