Dimensional Collapse
Dimensional Collapse occurs when a TARDIS's internal dimensions collapse in on themselves and the
Exo-Plasmic Shell suffers isomorphic mass-degeneration. Depending on the severity, this can reduce a TARDIS down to a black box about 2-cm square.
Internal Dimensional Collapse can occur
when a TARDIS experiences a severe trauma (such as the death of it's operator) or
because of the removal of the Time Vector Generator.
A TARDIS will "die" if it remains in Dimensional Collapse for more than a few decades. When the damage is repaired, a TARDIS will draw power from the Prime Eye of Harmony on Gallifrey and use it to re-grow. The internal configurations will probably be scrambled and redecorated. Without the Prime Eye of Harmony, it will take about a century to re-grow itself
using only the Artron Energy of its operator.
A TARDIS will need to be in close contact with a Time Lord during that time.