Hi Annette. I'm Greg, an installation specialist and 8 year Windows MVP, here to help you.
First you can try to Reset the PC choosing the cleanest option to wipe the drive. http://www.laptopmag.com/articles/reset-windows...
You'll need to back up your files as it won't save them but they may contain the infection so if you need to save the onboard files (and not a backup that's clean) then copy them to stick or external and scan with Malwarebytes before reimporting.
If the Reset wont' run or you're not happy with it then follow these illustrated steps in this link which compile the best possible Clean Install of Windows which will stay that way as long as you stick with the tools and methods given, has zero reported problems, and is better than any amount of money could buy: http://answers.microsoft.com/en-us/windows/wiki...
Make sure during the booted install to follow the illustrated steps to delete all partitions down to Unallocated Space to get it cleanest, then click Next to let it auto-create the needed partitions, format them and begin install - this makes it foolproof.
I hope this helps. Feel free to ask back any questions and let us know how it goes. I will keep working with you until it's resolved.