Wanted to play after months but am banned for another reason

[tuatara]

This is what happened to me, i stopped playing MW2 a months ago, uninstalled etc. (was at the last prestige for a very long time).
Yesterday i downloaded the 12 GB MW2 again from Steam and tried to play.

Message:

" Ignoring asset 'animtrees/destructibles.atr' of type rawfile,
between fastfiles patch_mp and common_mp
Cheat detected."

Which steps do i need to take, to be able to play again?
- create a new Steam account?
- Do i have to download the game again ? (takes some hours here) Or is this not needed?
- i could not find English MW2 keys here that i could buy? where can i buy them here and how to install them ?

For the record i know, that i was not banned because of the hack i paid here, (played to long with it, to doubt that).
but because my brother didn't know there was a good hack and installed a bad one

[leon101]

The steps to take: New steamaccount, New E-mail, New nickname and New key. Please make sure that nothing leads back to your old/banned account. I suggest to use google to search for MW2 english, you can also buy keys in steam -> steamshop.

[Snake Pliskin]

You can get any COD key here and other games at Digital Games DoubleDee runs it, has good prices, and excellent customer service.