It may be several things.

Try a different monitor or hook up to a TV and try that. Of course you'll need to change the input on the TV to PC for it to post.

Since the shop "fixed" it, I'd call them and ask what they did to fix it and inform them it's not fixed.

Thanks, we are going to check it with another monitor today...

If this monitor has previously worked with Win 10, I'd suspect the monitor may have reached the end. If it hasn't worked before with Win 10, it could be a driver problem (common with Win 10 and old displays). Solution is the same, a new driver may be needed.

Find another tech when you can - what you've described that was done is peripheral to the problem (as in, "if you don't know what to do, at least do something"). When it was "working fine", was he using your monitor or his own?

Edit-

Ooops, typo above. Should read "Solution is the same, a new monitor (not driver) may be needed.

He was working in his shop with his monitor.. Another thing I discovered today is that the fan isn't run nun and it is very warm around the vent.

Has this monitor worked with this PC with Win 10 before?

Yes , I up graded to Windows 10 last fall when it first came out.. And have been the same monitor.. Never have had any problems till last week.

How old is the PC? I guess it's possible there's a problem with the signal (or lack of signal) being output through the video connection for the monitor, but if the tech thought everything was okay while using a different monitor, that suggests the problem is your monitor. Borrow one from a friend or family member, or buy a new one from a store that doesn't charge a return or restocking fee, and see what happens.

If a new monitor resolves the problem, contact the tech and ask for a refund.

Got'cha I'll report back.

The computer is about 4 years old, the monitor is a few years older.. One thing I am wondering is if maybe the fan not running on my PC, as I mentioned above earlier could be the problem.. .

Sure, could be the PC going south as the problem, or in addition. That's easier (though not necessarily less expensive) to deal with - make sure you have anything important backed up, and after that, it'll run until it stops.

See if anything here might help, also if the fan is not working the computer can overheat and cause just about any problem.

https://www.freeflour.com/windows-10-black-screen-with-cursor-no-cursor-after-login/

but he didn't notice the fan not working?

He didn't say as far as I know, my husband picked it up. When I talked to him on the phone he said everything was working good after he worked on it.

Ok, I just clicked on the link that zep516 suggested, the comments..I heard the I pushed the cntrl once, and put in my password and pressed the enter and heard the log in and saw my name, and then it went black again.. So something "tried" to happen.. I am taking it back tomorrow and hopefully maybe he can fix it..