Well, it turns out that Microsoft did away with the Guest account in W10; so he didn't create one or turn it on, he changed your account permission from
Admin (Owner) account to a limited account, which Microsoft calls a
"Standard User". This type of account can fully use the computer such as running programs, using the Internet, changing personal desktop settings such as Wallpaper and Screensavers, icon layout, etc. but they cannot install new programs onto the computer with the Admin putting in a password to do so. No modifications are allowed to the Registry. This is similar to the Guest user in earliers versions of Windows from Win8.1 and older.
Given that information, there are programs that will allow you recover your Admin account permissions, but they require expert skill typically to use. If your personal data (Library folders) are backed up to external media somewhere, and that's not a concern, you can try the Windows Recovery PE disc/usb method to fix that account; but this also requires quite a bit of computer skills. The easiest way of course, would be to take your computer to your local Computer Pro or repair shop and pay a Tech to do this for you. If that's not an option or you can't afford to do so, another good option for you
*again, as long as your data has been backed up* is to use factory Recovery Media such as Discs or USB that should have been made when you bought the computer and first turned it on. Most modern-era computers made in 2009 or later have a hidden partition on the hard drive where a factory Recovery image is stored and can be accessed as mentioned by neemo using W10 bootable media (DVD or USB) as mentioned. However, this only works in about 50% of the time or so, and it's not a guaranteed solution but one worth trying before more aggressive methods are tried. If none of these work, and you don't have Recovery Media or you lost it, or purchased the computer from someone or received it as a gift (you were not the original owner), you can contact the manufacturer by visiting their website or phoning them up and ordering the Recovery Media (DVD or USB) for a fee or
$29-$99 US. You'll get them in 1-3 weeks in the US; longer overseas. This would allow you put back your computer to what we call
OOB (
Out-
Of-
Box) condition which is how the computer looked when you bought it new or when it shipped from the factory new with all the correct drivers and factory supplied programs and utilities.
If you have to go this way, and it works 99% of the time, you'll have to reinstall
ALL your programs that you had on that computer, such as Microsoft Office, Adobe CS Elements, Photoshop, etc. via install disc, usb, or via re-downloading all of them from the Internet where you originally purchased them or found them if free.

Once that is done, you'll have to copy back or restore all the data folders mentioned above into the correct places or library folders you originally had them in. This will fix your problem,

but it's typically weeks of work to do this complete rebuild, but is often cheaper than paying a Tech to do it for you.
Best of luck,
<<<BIGBEARJEDI>>>