see if you have a config file first and make a backup of it.. if you don't, maybe your tqvault has an option to change TQ path.. if you don't have config file and tqvault doesn't open, that is more difficult but still there is a way i think.. if you have config file, try to open it with a text editor (notepad will do).. then look for a line/s that says TQ path or something like that in it
like C:\Games\Titan Quest