The TARDIS shut down and died along with him. When Ace retrieved the TARDIS key from the Third Doctor's body, it had become isomorphically neutral, meaning anyone telepathically authorised could bond with it to activate and gain access to the TARDIS. When dormant, the TARDIS' interior dimensions were only enough to contain the console. When Ace activated it by placing the TARDIS key in a slot in the console, it connected with her mind and recreated the interior dimensions. (PROSE: Blood Heat)