First off, have you tried updating to 12.1 ? - select Updates from the Help menu
When looking at the thumbnail grid, do you have Media tab selected at the top? If you click on one of your album names do you get the message "No media to be displayed"?
It could be that you have a filter applied. Click on the All Media button at the top and then click on the album name again.
The problem with trying to add a new image into an existing album is usually resolved by first creating a new dummy album. You don't need to add anything to it and you can delete it later but it should then allow you to move new images into the album.
The way you filter by tags has changed since version 8. In version 12, if you hover over a keyword tag, you will see a small > appear to the right, click on that to select that tag as a filter.
Hope that helps