What OS are you using? Hammer only exists and works on Windows. If you are using Windows, then I suggest verifying your game files (right click on the game in your Steam Library, click Properties, go to the Local Files tab, click Verify Integrity of Game Files). If you're not on Windows, you can use WINE or something like that
If this is your first time logging in after the migration (Feb 8, 2022), you must reset your password to log in. Follow this guide if you're having trouble