This is a major problem. But no worries, I am positive I can help you.
What you need:
1: An external Time Machine/iCloud backup or no important docs currently saved on your Mac.
Instructions:
1: Restart your Mac in recovery mode. Press Command + R immediately after starting up. (Intel) Start up your Mac and continue to hold the power button as your Mac starts up. When you see the “Loading startup options” text let go of the power button then choose “options“ and continue. (Apple Silicone)
2: Enter your password in the user field, if necessary.
3: Select Disk Utility in the four options, then click Continue.
4: Select the disk closest to the top of the menu bar, then click Erase. In the pop-up select your desired name in the first field, APFS in the second, and GUID Partition Map in the third. Then click Erase.
5: Quit Disk Utility (Command + Q or select Disk Utility at the menu bar then choose Quit)
6: Choose “Reinstall macOS <Your macOS Name>”
7: Click Continue.
8: Click Agree on the Terms & Conditions and if there is a Pop-up click Agree on that, too.
9: Select the disk that you formatted a few minutes ago, then click Continue.
10: Wait for your computer to Install and Restart. Note: Your Mac may get hot when Installing and Restarting.
11: Set up your Mac the way you want it, then when it says “Restore from Mac, Time Machine Backup, or a Windows PC.” select “Restore from Mac or Time Machine Backup” Then click continue. Then Time Machine Backup. If you have an iCloud Backup you may need to restore later.
12: Plug in your Time Machine Backup disk then wait for it to appear. You may need to Refresh if the button is there. If there is no Refresh button and it can’t find your disk, make sure it’s plugged in all the way and then go out and back in. You may also try different ports if the problem persists.
13: Continue setting up your Mac.
The Problem should be resolved. If not, Take your Mac to Apple. You may need your original receipt as proof of purchase.
Hope I could help!
