You may have already tried this, but go to VPS Control Panel, reboot the server, wait a few minutes, go to Virtualmin (if Virtualmin throws error wait a couple of more minutes for server to reboot), restart Apache, start any services that were shut down by the server reboot. May or may not fix your problem but this is something I try when things completely cr*p out on me. Another advantage of trying to reset things in this manner, (IMHO), is that Virtualmin will usually self diagnose and tell you what service is problematic at the moment.