I would skip paying for/worrying about the diagnostics and just wipe and re-install, as the dx will likely cost you more. I understand that you don’t want to do this yourself, but it really isn’t that complicated - there are tutorials all over the web, or perhaps someone here would help walk you through.
In short - back up your files to external or cloud drive, be sure you have your product key, download windows 10 (I’m guessing you’re using windows) install file (iso) and burn as image to dvd or create bootable flash drive, boot to bios (usually f2/f10/f12 at boot - you can look this up for your particular sys), set boot order to your chosen media (DVD or usb), exit to boot, and follow the instructions when windows loads.
Or if you want to wait until the 3rd week of July or so, I’ll be passing through your area on my way to Asheville :D. But I don’t know why you’d trust me (or anyone else on this site) more than geeksquad, or some other local technician. In the meantime, if you’re worried about someone tracking your movements on the internet or etc, you could easily boot from a live linux distro (again iso, DVD or flash drive) without having to reinstall… tails is an interesting option for the most anonymity - nothing would be recorded/might mitigate your security concerns. Best of luck!