Messages App not showing conversation list

This is a VERY strange problem. I'm running Mavericks, and for some reason the Messages app doesn't show any windows on startup, and can only display preferences and a single conversation. I tried creating a new user account and it worked fine with the same iCloud account for iMessages. I tried copying the com.apple.ichat.XXX.plist files from that user account back to mine but to no avail. I've also restarted several times. Any help would be greatly appreciated. The weird thing is sending messages works fine, I just can't see all of the conversations (and don't get notifications for new messages).
Thanks!
Stuart