Your best bet would be to create a Windows 7 SP1 disk. The link below contains links to download the ISO file for Windows 7. Make sure to get Windows 7 Home Premium SP1 English x64. I also provided I link to a tutorial for making the installation disc. Note that you will need either a blank DVD or a USB flash drive that you can boot from.
Official Windows 7 SP1 ISO from Digital River « My Digital Life
Windows 7 USB/DVD Download Tool
For installing, use the tutorial linked below.
Clean Reinstall - Factory OEM Windows 7