(redirected) Dimension Desktop infected with Cryptowall virus

My mothers computer has gotten infected with the Cryptowall virus.  She only uses it for email so there are really no important files to worry about.  However, I do want to do a clean-up on it with perhaps a hard drive reformat and then upgrade her anti-virus software.    The computer was preloaded with Windows 8 but there are no back-up disks to reinstall the OS.  Where do I begin?  Do I contact Dell with all of the particulars of here computer and somehow get a recovery disk?

Thank you!