Restart Hearthstone and HDT.

Right-click the HDT icon in the taskbar, and see if "No Deck Mode" is selected. If it is, unselecting it should fix this issue.

Or another common fix is opening HDT by right-clicking the shortcut option and selecting "Run as admin."

If the problem persists: See here on how to manually set up the log.config.

Problem still persists: Make sure the Hearthstone path is set correctly. options > tracker > settings > set hearthstone path (There were user reports of this not working, to manually do this: Close HDT, go to %AppData%/HearthstoneDeckTracker (Win+R, paste), open the config.xml with any texteditor and look for <HearthstoneDirectory>...</HearthstoneDirectory>. Set this to the correct path.The correct path is the one used in the Battle.net app options (Battle.net icon > Settings > Game Install/Update > Game Installation > Hearthstone)

Check if the log files are created at <HearthstoneDir>\Logs and written to. If there aren't any logs or if the logs are outdated:Unblock Hearthstone in your antivirus programs

Exit Hearthstone, delete %LOCALAPPDATA%\Blizzard\Hearthstone, start HDT and then start Hearthstone again

If you are using the same Hearthstone installation since beta, try reinstalling Hearthstone (see here)