DO (and other tools) can't start again

[Leo]

Check that you have not launched dopus.exe elevated, as that will block requests to open new windows:

Why NOT to run Opus as Administrator under UAC

UAC Support Directory Opus supports Windows UAC and will prompt for elevation when required to perform administrator actions. The program itself does not need to be run elevated, and doing so can actually cause problems (detail below). Opus also ha…