Civi seems to be working normally, but all dashboard items are showing 503 errors (ngnix).
Any ideas of what to check? Hosted on Arvixe.
Some issues with the dashboard have been fixed in the upcoming 4.7.11 release. See CRM-16035: Dashlet refresh can crash server / Replace use of HTTP_Request and CRM-17663: Dashlet code improvements for details.
There are quite a few existing questions on dashboard issues on this site - you'll find some good answers there I'm sure for dealing with CiviCRM below 4.7.11.
Once 4.7.11 releases, that should resolve your problem.