What do you mean by reset? Did you load the wrong save (e.g. auto-save, quick-save, area-save, assigned slot save)? If so, you might have just loaded the wrong save, but you should be able to correct the issue by loading the correct save (use the load save menu).
Did your character reset to zero? Zero experience, zero gold, zero items, etc? If so, this is a problem almost exclusively with pirated, hacked, or modified games. It occurs due to an error in the code editing process. It is not something we can help with on this forum. See forum rules.
Providing more detail might help. Device, version of game, where you got the game, etc.
MOD NOTE: Changed thread tittle to better reflect nature of problem.