I assume that you have a Win7 CoA from your first installation but you lack an installation DVD.
You can download an official Microsoft Win7 SP ISO from here:
Official Windows 7 SP1 ISO from Digital River « My Digital Life
Then you can reinstall Win 7 again.
I must agree with you, I did not care for Win 8 and have gone back to Win 7 myself - put it down to old age especially as I started with 3.1!