Your motherboard is set up for UEFI, not plain BIOS. UEFI writes a GPT structure on the drive. Once this structure is on the disk, a Windows 7 install disc can not remove the structure. To fix this take the drive out of a UEFI system and set up your computer for just BIOS. Use a program like Paragon the examine and fix the drive back to a MBR. Microsoft Windows 7 claims the drive is UNALLOCATED but the GPT structure is still on the drive. Once this structure is removed using Paragon, You should be able to do a successful build. I spent 6 days working on this problem. Please see my other posts.