The alternative is to get a new HDD, reinstall Windows onto it, install AV software and then get the data of your old HDD.
I suggest a new HDD as I suspect there is something nasty on the old one, and that you don't have any backups of your data so you can't reformat it as part of reinstalling Windows. If you really have spent hundreds of $$ then the price of a new HDD will come as a pleasant surprise!