Now that computer is fine, I would advise you to create a system image onto either DVDs or an external HDD and do the same before running the program on a machine.
It is a reputable repair program and nothing like the myriad of tune up programs that are out there, although it has just had a major fix which was causing a problem on Win 10 v1803.
BTW - Which version of Windows are you using it on ?
Hold off on buying a licence just yet until I get back to you.