Wipe it only if it's dusty on top. JK. No, just format. The easy way is just to put your windows disk in and boot from the disk. When it asks which partition you want to put windows onto, you can can first delete the old partition, create and format a new using the entire allowable volume, then install on the new partition.
Before you format though, make sure you back up all the files you want to keep including any COD profiles.
From reading what you are saying about your issues, I believe formatting and starting clean is the right way to go. It's always a bit of a headache to reinstall all the windows updates and software again but you at least start fresh with no extra shit. Once you have windows on your PC and up to date, put MSE on it for antivirus and something like Malwarebtyes for antimalware. I use that combination and have no issues. More importantly, just stay away for all that porn.
PS: BACK UP ALL FILES YOU WANT TO KEEP BEFORE YOU FORMAT. Post back if you need help with COD profile locations although I believe the XI downloader does a decent job with that.