Arduino suddenly not working?

I'm just a beginner and but the elegoo super starter kit. for the past 4 days or so ive been having a ball doing all the projects that come with said kit, steadily chipping away at each course. last night I did lesson 11 or 12 that dealt with relays and it has you hook up a motor to a relay so you can get an idea of how it works. long story short I did the project, it was very cool and worked as advertised.

today I jump on the computer and start the next lesson but, when I go to load the new code onto my Arduino it gives me an error message

Serial port 'COM3' not found. Did you select the right one from the Tools > Serial Port menu?

when I go to check the "Tools" menu the Serial Port section is grey and not able to be accessed. I have not changed anything from the last time I used it to attempting to use it now. why can I not load any new code? the Arduino does light up and the "on" light is light.

Grrr another elegoo...

Few questions if you dont mind.

OS ?
IDE version ?
Do you see the Arduino listed in your hardware configurations anywhere ?
Have you tried another USB cable ?

WARNING.
Please dont USB 3.0 with Arduinos as they results are a little unpredictable.

Also anything else you can add at all. You might be surprised at what could help.

I have no idea what an "elegoo" is, presumably a brand?- but whenever I have any errors like that it's never been a permanent thing and so far if I'm certain the settings are correct, a total power off/ power on has done the trick. (It has happened that I had just fired up, like OP presumably did on a new day, but a re-start somehow aligns the planets.)

edit: went to elegoos' site. Not sure I'd trust a vendor that uses fake Latin Lorem ipsum style text on their face to the public :wink: