Sounds like you have a more basic network problem, forget about domains vs workgroups for the time being.

A vlan is a logical division of a switch(es) into separate segments, which means you need a router to route between vlans, but not within the same one. You need to identify what hosts can ping what hosts, and if not are any hosts on different subnets(ipconfig). Make sure each host can ping the default gateway as well. Come back and post your findings.