We have a Dyson vacuum cleaner. For ages it has been playing up so we bought a new bar. Put it in I did the carpet, still not picking up. Took it to pieces belt broke changed belt. Did carpet again. Today I hovered all downstairs again. Still not picking up. OH took it apart, jiggled about, put it together again still not working. Decided to take it to SIL. He'd lent us his spare one while he looked at it. I hoovered downstairs again. This one not picking up also. Realised rollers not going round. Discovered a switch that makes rollers go round. Did all carpets again. Still not picking up. Turn upside down and discovered why. The rollers were absolutely full of hairs and also a pair of tight wrapped around roller. The mound of hairs had to be seen to be believed. OH had to cut them with a Stanley knife to release them. There are four girls in the house all with long hair. Also two cats and three dogs. So not surprising things were so bad.
So I hoovered again and. This time it cleaned the carpets properly. Job done but I'm absolutely cream crackered.