My Dyson Dc37 recently had a blockage which made the power bar ( for carpets) stop turning. I found and cleared the blockage, but the suction wasn't enough to turn the power bat on again. I checked every possible blockage site, and cleaned the filter. I was able to get the bar running again after taking the purple thing out of the canister and tapping dirt/ dust out. Is this normal? Nowhere in the manual does it say that it should be cleaned beyond a wipe down. Is this something I should do on a regular basis? My machine is only about a month old and has only cleaned regular indoor household dirt

Yes, you should clean the filters regularly. Dyson's claim "the vacuum that never looses suction" is IMHO crazy. A regular filter cleaning will keep good suction *and* significantly prolong the life of the vacuum motor. Vacuum motors which are starved for air will actually draw more power/current, overheat (current & lack of cooling) and eventually burn out.

A video on the filter cleaning is:
http://www.youtube.com/watch?v=m8gMAWHCrVo
be sure to let that guy dry for a day -- you don't want any moisture entering the motor.

I'm not sure what exactly the "purple thing" is except for the filter though so perhaps I am misunderstanding your question. It is also possible and quite well documented that the funnels at the top of the vacuum chamber that form the cyclones can become blocked/impacted. this is particularly true when the vacuum is overfilled. Sometimes it is best to disassemble the upper chamber to remove impacted material or dislodging via "knocking it about" can be helpful! :) But I don't know how to test for blocked cyclone tubes.