I would systematically go through everything and wash/dry filters etc until you've gone through all potential probs.
Mine stopped working a few back - there was no suction but I then realised the pipe hadn't been pushed on the back properly.
Unscrew the brush cylinder and cut out all the hair/bits of cotton ect and make sure the bin is set properly where it should be.
If you can work out (if it is genuinly broken) if it's a specific part that's broken - then Dyson customer services were really amazing and fairly cheap when it came to me replacing the hose for my old one (at the time 10 yrs old).
The whole top handle and tube was only £28 quid and it was delivered the next day.