check on steam store page for 7d2d your hardware/software meets or exceeds all requirements
make sure your game is up to date on steam.. latest version . start 7d2d,, click on join game, . make sure you can search for servers (skip past the new server filter screen) select a server with no password and try to join it.. what happens?
keep in mind your first game join you will have to either create a map/world or download one.. this can take several minutes or tens of minutes .. depending on map size