Hello CarlLJ,welcome to the Microsoft community, I'll be happy to help you today;
I understand that you are having problems logging into the Microsoft Store.
Does your internet work well in other apps?
Initially I recommend that you try the fixes below;
Check if you are updated with the latest version of Windows 10;
Press Windows key + i and go to Update and Security;
Click Check for updates and do ALL pending updates;
Run the store troubleshooter;
Press Windows key + i and go to Update & security;
Click Troubleshooting and then Additional Troubleshooting;
Select Windows Store Apps and click Run the troubleshooter;
Clear store cache;
Click on the WIndows search bar and type: wsreset press Enter;
Reset the network;
Press the “Win + I” keys together to open the Windows 10 “Settings” screen and enter “Network and Internet”;
On the new screen, under “Status”, slide the screen down and click on “Network Reset”;
Now, click on “Restore now” and confirm the beginning of the process;
Before restarting the PC, perform a clean boot;
Press the keys: Ctrl+Shift+Esc to access the task manager;
Click Startup and disable all programs that start with Windows;
Restart the PC and check if the problem still persists;
See you soon!