Since you already formatted C drive building recovery media is out of question. I highly recommend creating recovery discs or disc image before repartitioning HDD.
If you really want to get rid of Win8 and don't care about coming back to it, please follow the steps.
Firstly you need to enter in to BIOS and make sure "SecureBoot" is turned off. Location of it may be different from model to model but usually found under boot settings.
Secondly clean all partitions of your HDD. You can either use any free partition CD or diskpart from Win7 DVD repair command window to do that. Here is a how to guide for Diskpart : http://www.pronetworks.org/forums/using-diskpart-on-the-windows-7-dvd-t112571.html
Instead of deleting partitions one by one you can use "clean" command to clear partition table.
Here is the download link for Partition Wizard home edition boot CD : http://www.partitionwizard.com/partition-wizard-bootable-cd.html
It is a linux based GUI live CD so you can easily edit partitions without much explanation.