There are several reasons you could have login issues, below a few troubleshooting steps to take.
You can also check for any outages with Jobvite Here
1. Check your internet connection and ensure you're connected to a strong stable network.
2. Check what browser you're using, Google Chrome is the ideal browser to be using. Make sure you're not signed in across multiple browsers.
3. Clear cache and cookies for all time in the browser you're using. You can also try in incognito.
4. Your user name should be your email.
5. If you use SSO make sure there were no changes with your SSO environment. This can be verified with your internal IT.
6. If you're not using SSO you can request a password reset. This will trigger a password reset email to be sent to you.
7. If after verifying these things you're still having login issues please submit a ticket with Jobvite support, or work with your company admin to submit a ticket with Jobvite support on your behalf.