I bought a used laptop for my son.

1. It's an HP laptop: There is no serial number on it's exterior (the sticker has been removed).

2. When I go to My computer > System it says the System Manufacturer is Toshiba.

3. Internet access is OK for general surfing but when he gets on the online game that he likes (World of Warcraft) his username is immediately hacked... but AVG finds no problem on the system.

So in short, I'd like to format this laptop and start it with nothing... then install Windows and go from there.

What steps do we need to do to get it done?
Or
What else do y'all need to know for me to get it done?

Thanks!

You'll need a Microsoft Windows CD and its valid key. Boot to CD and select new installation which will format the hard drive before installing.