There are a couple of things that could be causing this problem. The most common resolution is to quit the application and clear the App Data folders for the softphone from your PC. It sounds like you may have already attempted some of this, but just in case, here are some good directions:
Troubleshooting Desktop App crashing or blank screen:
1) Uninstall the old Legacy: If you still have it installed onto your PC.
2) Make sure you have the most current version of the new softphone installed.
3) Logout & Close the new one ... also close it from running in the background from your task bar.
4) Deauthorize the PC (see Image 2)
5) Go to Computer > Local Disk (C:) > Users > pick user > Appdata > Local > RingCentral > Delete the two folders. (see Image 1)
If you don't see "App Data" at the top above Contacts just click on the navigation bar above, enter in "\appdata" (mind the backslash), then hit enter.
6) Log back in and test.
Once you log back into the softphone, it will automatically authorize that PC, so no action is required from you on that part.
If this does not resolve your problem, we recommend calling into support at 888.898.4591 for additional troubleshooting. Alternatively, you may open a case with our support team for further assistance.