As Ana says, modal verbs (can, could, must, may, might, will, would, shall, should) are followed by the base form of the verb. The main verb is not conjugated when it follows one of these verbs.
Also note that modal verbs don't have a 'to' either before or after them. The 'name' of the modal verb is simply 'can'. The verb 'to can' has a different meaning - this is what is done when products are put into cans, as in 'canned fruit'.