Please try fully exiting Opus (via File / Exit Directory Opus) and trying again.
If that doesn't work, turn off automatic update checks (un-tick Preferences / Internet / Updates / Check for news and program updates), then close Opus and try another time.
The issue may be that if there's already an update check going on in the background then pressing Check Now doesn't do anything. Why the update check isn't completing or is taking so long is a separate issue, but let's see if I'm right about the first part first.
If neither suggestion above makes a difference, there are some other ideas in this thread which may be worth considering.