Replacement motors for bathroom fans

Look on the motor or up in the fixture you took it out of.  It should have a label with the name of the manufacturer, the model name and model number.  In addition, they will sometimes give the address of the manufacturer, the ratings of the motor, and other information like dates, patent info, etc.

Then do an internet search for the manufacturer.  If they still exist, you're done.  If they don't exist, you have to find out who is making the replacement motor now. 

If it's really old, named Ventrola, you can still get a replacement. 

how do i know its the motor that need to be replaced.  And where do i get the same kind that I have

Check to make sure that when you turn the switch on that power is actually going to the fan by checking the wires.  You can get a touchless tester at some place like Radio Shack or Home Depot for about six dollars (US$) if your fan doesn't plug into it's box with a regular plug (many of the older ones do).  If it has the plug, you can plug radio or lamp in and see if it comes on when the switch if turned on.

Once you know for sure that the fan is bad, loosen the screws holding it in and pull the fan out.  check the fan and the box for a label that names the manufacturer and gives the model number of the fan.  Then do an online search for the manufacturer.  If you can't find them, ask at Yedda.com or Hometips.com for help.