I would try these steps first, please do this ASAP because the issues can quickly go downhill and make recovery more difficult. The revert to 2.3.7 is in the advanced menu in the diag tool.
If you still cannot update after that then use the diagnostic tool to update. First use the Download Latest button, then use the Restore Previous... button (it can update as well.
Once you are updated I would do a reboot, click advanced then rebuild database and purge logs.
