A bizarre, life-changing, even cosmic event scrambles your powers such that you now have a whole different set of powers. In game terms, you strip your character of everything they bought with CPs, including Ads, and buy a whole new everything. The new powers replace your old ones. You retain your Natural Ability Scores and anything you acquired through your levels and/or your class (e.g., HPs, feats, skill points, ability score increases from levelling, etc.).
A temporal anomaly (or whatever) literally rewrites your personal history such that you can rebuild your character from scratch. The character must be more or less the same person, but can have a few major differences; e.g., swap genders, change ethnicity, alter birthplace, etc. Everything else can be completely different: different class choices, different powers, etc. The world around you is oddly unaware of the change. Everyone remembers you in your present form. In cases of logical contradictions―your former self used flight to save a city whereas your current self can’t fly―people dimly recall events as they originally happened, but don’t perceive the contradiction.
NB : Players can take this enhancement only with the GM’s permission and with the approval of their fellow players. A Reboot is a major change to a hero team and can potentially create a lot of confusion. It can also be a hilarious and bizarre and fun when the world just doesn’t seem to remember that “you” used to be a red-haired, axe-wielding Valkyrie, but now “you” are a robot made of sentient diamond shards.