You can verify your login information on the Account Information tab by clicking Menu > Options > Account Information. Also please verify if you can login to your RingCentral Mobile account.
If the information above does not help to resolve the problem and your Softphone still displays, Unable to connect - Connection failure, please check each of the following.
1. Verify that Microsoft Internet Explorer is configured to connect to the Internet - The Softphone uses Microsoft Internet Explorer's Connection settings to detect and connect to the Internet. If you are not using Internet Explorer and it is not configured, please change its Connection settings.
2. Verify that you can connect to the RingCentral web site from your computer - Simply open any internet browser, enter http://www.ringcentral.com into the Address bar and click Go.
3. If you have a personal firewall, verify that it is not set up to block the Softphone (application name "RCUI.exe") from connecting to the Internet.
If you still unable to fix the problem please contact customer service at (888) 898-4591 and provide them the information displayed at the beginning of the page: Error Code,Technical Description and Session ID (if available).