The computers running the server occasionally (rarely) crash or have connectivity issues. Usually these are resolved fairly quickly; at worst, you might have to wait a day or so.
If the game seems to have crashed but you can still access the server itself, then there is an option to do a hard restart of your game. You will have to pick up your character from its last backup in that case.
Hoping to win with every class, doomed. Archer, Barbarian, Bard, Beastfighter, Druid, Elementalist, Farmer, Fighter, Monk, and ULE Priest down.