There was "infrastructure transition" in November 2018 of backend servers and it caused outage of services for more than a week. If you imported your wallet into Light or web wallet software before this outage, it may become unusable. If you see only never ending spinning Merit logo like on the picture below, it's probably your case.
To fix this, you have to clear data of your web or Light wallet. In case of Web wallet you need to delete data and cookies, use Google to find the way how to do it. It's specific for each browser and OS. Also you can use anonymous window for fast access to your wallet.
Warning: This process will remove your wallet from Lightwallet software, you need your 12 words backup phrase to recover it!
If you were using Light wallet and see that spinning logo, follow these steps to clean your data:
1. Open Developer Tools window
You can do it in menu: Window -> Toggle Developer Tools or with keystroke CTRL + SHIFT + I on Windows or CMD + ALT + I on MacOS.
2. Choose tab Application
In Developer Tools window find Application tab, it might be hidden under double arrow button.
3. Clear data
Choose Clear storage from left menu, check all checkboxes and press Clear site data button.
4. Restart and import your wallet
After cleaning your data you'll be able to use Lightwallet again. Restart the application, choose the second option and import your wallet with 12 words again.