Check if Steam is Down - Check http://www.issteamdown.com/ to see if Steam is truly down, if it is, you may have to wait a bit until Steam is able to get their servers back online. Steam Downtime is usually under 30 minutes. If Steam servers are up, your local Steam may have logged out or have been put into Offline mode. Don't Starve Together MUST be in Online mode to register your account.
Ensure a Stable Internet Connection - Check to see if you are able to connect to the internet. If you are connected to the internet wirelessly, try connecting using a wired internet connection.
Disable Steam Overlay - If the Steam in-game internet browser is not opening with the Don't Starve Together account creation page, you will have to disable Steam Overlay.
- Right-click Don’t Starve Together in your Steam library > “Properties”;
- In Properties > go to “General” tab;
- Un-check “Enable the Steam Overlay while in-game”
- Click on the “Close” button to close the properties window; start the game.
Doing this will force Steam to open up your default web browser (ie: Chrome, Safari, Firefox) instead of the Steam in-game browser the next time you try to create your account.