Electric motors are pretty tough. Remove the existing one (plus filter if present) and get rid of any crap that's collected. If necessary, clean up the motor so that it rotates freely and maybe check the carbon brushes make contact with the commutator (and generally look ok).
Refit the motor (and a clean filter). If it still doesn't work, even on maximum speed, get a replacement from a scrap yard or from ebay.
You might also consider testing the motor with jump leads direct from the battery, just to make absolutely sure it's dead before replacing it.
Also bear in mind that when a motor burns out, it may take a fuse with it.