Your Roomba doesn't understand what a cord is, or a sock -- or any of a number of other things that, when consumed, will allow him to meet his maker. Cut your Roomba some slack; he's only trying to help.
A sure sign of cleaning head module (a.k.a. brush assembly) failure is that your Roomba no longer sounds like a jet engine. In other words, it will be noticeably quieter than before.
To test the brush assembly, sprinkle some crumbs (cereal, crackers, tiny obscure objects, etc.) in front of the Roomba, turn it on, and see if it picks it up. I've provided a video on how to accomplish this complicated task.
Loosen the 4 screws on the bottom cover of the Roomba and remove the bottom cover. The screws are clipped from beneath so they can't be fully removed, but they don't need to be.
Loosen the 4 screws that hold the brush assembly in place. These screws are also clipped from beneath, but your new assembly includes some pre-installed!
Next, remove the dust pan and, finally, lift the module out of place. Lastly, throw the module in the garbage, angrily, because it sucks.
As always, assembly is the reverse of disassembly. While your Roomba is open, be sure to clean out the gunk that you'll notice has accumulated.
Don't forget to regularly clean your brushes from now on -- it only takes a few minutes, but it can save you a lot of money in the long run. Enjoy!