Dyson vacuums are known for their excellent suction power. However, all of this suction is useless if the brush bar at the bottom of your vacuum doesn't spin and lift the dirt off the carpet. The most likely reason for this to happen is that your Dyson has a broken belt. No worries. It is fairly easy to replace it. Most stores that stock Dysons will also stock replacement parts for them. If not, you can order a belt directly from the manufacturer.
Unplug your vacuum cleaner. Stand behind it like you would if you were vacuuming. Then pull it toward you, tilting the whole machine until the handle is lying on the ground. Walk to the opposite end of the vacuum so that you can see underneath the base (the part with the wheels on it).
Look for three plastic screws on this piece that are the same colour as the accent colour of your Dyson (the colour that isn't grey). They will be attached to the base plate, which is the part that covers the brush bar. Turn each of the screws counter clockwise with your flathead screwdriver. You only need turn them a quarter turn. They should remain attached to the vacuum.
Pull the base plate toward you to remove it. Now you can access the brush roll. Look toward the left side of it, about four inches in, and you will see a groove where the belt wraps around it. If your broken belt is still attached to the vacuum, pull it out of this groove and discard it as you pull the brush roll out. You will notice a slot in the vacuum right behind it.
Pull any hair or other objects stuck in the brush bar out and discard them. Feed the brush bar through the new belt as if you were threading a needle. Stop when the belt gets to the groove and push it tightly up against the bar. Push the remainder of the belt into the slot in the vacuum cleaner as you put the brush roll back in place.
Slip the end of the belt not touching the brush bar around the motor shaft, which is the metal rod that lies to the right of the bottom of the vacuum's hose. It will take some work to get it on since the belt needs to be taut.
Turn the brush roll with your fingers to make sure it spins without getting snagged. If it doesn't move freely, pull it off and try again. Replace the base plate and lock the screws back in place.
If you don't have a screwdriver, you can also use a coin to turn the screws. These instructions are similar for all Dyson models. Check your owners manual for any slight differences.