Whenever I sleep in my bed to return to the Imperial City, my game crashes. I have tried deactivating all mods, but it did not work. I also checked the UESP page on the quest (http://www.uesp.net/wiki/Oblivion:An_Unexpected_Voyage), but that did not help me either. I also tried using the console to set stage, but the game crashes whenever I reach the stage in which the ship has returned to the Imperial City and I am supposed to talk with Ormil.

I have no idea how to complete this quest, as I've tried everything. Does anyone have any ideas why this is happening?

Is the quest "Elven Maiden" active in your quest log?

That can cause the crash. Some people still experience this even when the quest isn't active, but it's worth checking.

Edit: I guess since you said you read the wiki..
Darn well, that's all I got

I haven't even joined the Thieves Guild yet. The crash has something to do with reaching that stage of the quest, not the sleeping itself, since I still get the problem if I use setstage.