If you have an Win 7 OEM full install disk, just let them install Win 8. When you get the laptop back, format the hdd and do a clean install of Win 7. The only potential problem might be any specific drivers this laptop needs that are not in Windows 7 - but if they took your laptop in to start for the purpose of doing a Win 7 install and then found a hdd problem and are now telling you that they can't do a Win 7 install on it, it sounds to me like they are screwing you around. I am not sure why they won't do this for you unless they are being told by Microsoft not to but - that is why they took the laptop in for service in the first place!
