Clean Up Computer

I have been having sever data corruption issues with the game World of warcraft. i have run every diagnostic software known to me including checkdisk (windows xp sp3) Microsoft’s memory diagnostic tool and seagates hard drive diagnostic tool both windows and bootable CD versions and every diagnostic comes back squeaky Clean and ive even swapped my ram entirely. I have done a full system restore on my computer and i still cant get a stable install which leads me to believe i have a hard drive issue yet it passes every test. so basically my question is as stated above, is it possible for a hard drive to be going bad yet not fail diagnostics. If so is there any way to verify or at least gather further evidence that its the hard drive before i spend money on a new hard drive. (note it appears as if only world of warcraft is currently effected, i suspect its highly complicated file system is more likely to be damaged by a failing hard drive)
i have installed all patches and all blizz will tell me is its a hard drive issue or a ram issue. and it cant be a virus as i JUST reformatted my hard drive. i have also updated every driver in my system. and while its not a data coruption issue limewire shuts down when i attempt to preview a file