OK, you have decided that the HDD contains NOTHING you want to save and it can all be wiped out for a fresh install of Win 7. Do you have a Win 7 Install disk? That disk has the tools you need for the whole job, so here's the sequence.
1. Ensure your 1 TB unit is the only HDD in the machine, and there is an optical drive unit. Place the Win 7 Install DC in the optical unit. Boot the machine and go immediately into BIOS Setup. Usually this means you hold down the "Del" key while it starts to boot and after a few messages it will suddenly show you the opening Setup screen.
2. Go through the Setup menu system, usually to places like Attached Peripherals and Advanced. Where you have the SATA device configuration options, check that the port you have connected your drive unit to is Enabled, and also the port that has your optical drive. Close by there should be a place to choose SATA Port mode settings like IDE (or PATA) Emulation, native SATA, AHCI, or RAID. Choose AHCI if you can for your HDD unit, second possibility native SATA. Now look for where you specify the Boot Priority Sequence. Set it to use the optical unit as the first choice, the 1 TB drive as the second choice, and NO other choices. Save and Exit from here to finish booting.
The machine should boot to the Win 7 Install Disk in the Optical drive. First step will be to use the menus to go to the only HDD unit there and Delete any Partition it contains. Make sure you Delete all of them, one at a time if necessary. Now you can proceed as if your HDD is a brand new empty one. Go though the normal Install process, probably choosing to use ALL of the space on your HDD as one large volume on which you want to install your OS using the NTFS File System. From here on it should just be a plain Installation process that ends with you having a machine running Win 7 smoothly.