I downloaded one of those "diagnostic" programs once, but NEVER again! It said that we had different things wrong with our computer and the next step was to pay for program to get rid of these problems. I decided not to do that and tried to uninstall the "free" program and it wouldn't uninstall. At the time, we were running Windows XP, so I ended up doing a "recovery/reformat" of the hard drive.
Only downloads I do anymore is for "updates" and "new versions" of programs I already have on the computer. If I wind up with a computer problem, I will go to different websites that discuss the problem I'm having. If that doesn't help, I'll take to somebody who knows more about "diagnosing" than I would. I'm a "techy"...........to a point. After that, I let the Professionals take over.