Try the following steps in order:
Check your Wi-Fi or mobile data connection.
Fully close MyTunes and open it again.
Restart your phone.
Update MyTunes from the App Store or Google Play.
Update your device operating system.
If the problem continues, reinstall the app only after confirming that you can access the same account or identity again.
If MyTunes still will not open, contact support and include your device model, operating system version, app version if known, when the issue started, and a screenshot or recording if possible.
Do not create a new account while troubleshooting unless support asks you to. Your Library, purchases, and creations can depend on the identity used to access the app.