I have an Electrolux Aerus 2100 canister vacuum. When I

It takes the "C" (canister) bags made by Home Solutions for Aerus Electrolux vacuum cleaners.

This actually cover several models of Aerus and Electrolux canister vacuums. Models covered include: 2100, Epic 6000, Epic 6500, Aerus Lux 5500, Aerus Lux 7000, and Aerus Lux Legacy. Be aware that some of these models may still be under warranty. Any disassembly of those machines will void the warranty. Use of non-genuine bags also voids the warranty. Use only Home Solutions Aerus/Electrolux bags.

First, turn dial on top of vacuum counter-clockwise so the smallest dot lines up with the arrow. See if it stays on. If not, detach hose and turn vacuum on. Place palm of hand over intake. If it turns off, it's possible that the tubes connecting to the CVA are clogged and simply need cleaned. This is most often caused by using "made to fit" Electrolux bags. Dust is sucked through the bags and into the motor compartment of the machine. All interior parts get covered in dust and need to be cleaned. If this is the cause, the vacuum is best cleaned and repaired at an authorized Aerus Electrolux store. If the vacuum shuts off, or won't turn on before placing hand over the intake, it's probable the control valve assembly is bad and needs replaced.

Another cause is an overheated motor due to clogged screen at back of bag well, full or clogged bag, dirty afterfilter, bad wiring/connections, clogged hose, clogged power head, or bad motor. It depends largely on the type and model of cleaner. Clogged wands are also a possibility, but unlikely.

Check and clean screen at back of bag well.

Replace bag. Make sure it's a genuine Electrolux bag made by Home Solutions.

Check and replace afterfilter if necessary. These should be replaced after every six bags.

Broken and worn wiring connections are often found in the hose ends due to abuse and normal wear and tear. You can check the continuity of the hose using a continuity tester or multi-tester. If a multi-tester, turn dial to one of the Ohm settings. Place one probe into one of the terminals on the end of the hose. This will be referred to as T1. Touch the other probe to each of the terminals/connections on the other end of the hose. These will be T3 and T4. One of them should read zero, the other should read infinity. Repeat this with the other terminal, which will be T2.

Drop a marble in one end of hose and let it roll through. If it doesn't roll through, the hose is clogged and needs to be cleared. Plug hose into the exhaust port of the vacuum, place other end in the in port. Turn vacuum on. This provides a blowing and sucking action which should clear the hose.
Detach hose from power nozzle (PN). Drop a marble into the wand end of PN. If it rolls through, it's clear. If not, there's probably a clog behind the brush where the intake opening is. You may be able to reach this through wand end with needle nose pliers, or either end with a knitting/crochet needle or a bent coat hanger.

If none of these "fixes" provide the answer to the problem, it should be taken to the nearest Aerus Electrolux store for diagnosis. Repairs or checks involving disassembly of the vacuum should always be done by an authorized Aerus Electrolux service technician.

The store nearest you can be found by following the instructions at the below listed link:
http://www.aerushome.com/storelocator/

Due to problems getting it back together, I don't recommend taking it apart. Dismantling and reassembly the cord winder assembly is also complicated and most people have problems doing so correctly. I strongly suggest taking it to an authorized Aerus Electrolux store and spending the money to have an experienced tech do the job. However, if you do decide to try this yourself, there are instructions on the second site below. The first site is for locating the nearest Aerus Electrolux store.
http://www.aerushome.com/storelocator/
http://www.howtomendit.com/answers.php?id=2297

You can buy the hose at an authorized Aerus Electrolux store. If near enough, they will deliver, if too far, they can ship it. The nearest dealer can be found using the below link. Just follow the instructions.
Just provide the model of the machine. They will know what hose you need.

http://www.aerushome.com/storelocator/

Dismantling the vacuum probably won't help much, and reassembling can be a bear.
To check the intake, remove bag and look into bottom of bag well. It there's a filter there, remove it and check intake at bottom of bag well. Clear if there is.
The afterfilter on a canister is located beneath the air diffuser grid on the top of the machine where the tools can be attached. Remove this cover and there should be a white filter. Yours is probably black, or at least real dirty, if it's never been changed. This also blocks the airflow, reducing suction, and potentially damaging the motor. Extremely dirty filters are an indicator of how much dust is getting into and through the motor. This is usually caused by using generic bags rather than the genuine Electrolux, now Aerus, bags.
It is also an indicator of another internal problem on some other Aerus and pre-Aerus Electrolux vacuums.

If the bag full light keeps coming on, you can first try adjusting the dial on top of the vacuum cleaner. If that does not work, then you need to change the control valve. This is an internal component of the canister and is directly below the dial. You will need to follow the instructions on a previous post to open the Electrolux plastic canister vacuum, and remove the bage cage. Once you remove the bage cage you can change the control valve, and this will solve your problem with the bag full indicator.

This is exactly the symptom you would expect from a defective bag control valve. The actual control valve sits under the dial on top of the vac and often cracks internally. It can be replaced in about 15 minutes by a good tech with genuine parts from AERUS Elctrolux dealer or repair center.
You can open the vac front to rear like a **** shell by sliding the bumpers out the front with the bag door open, however you must be careful not to disturb the wiring harness and to mark wiring locations. The body must be carefully realigned for closure. If it is not perfect you will not be able to slide the bumpers back in.

Check to be certain the thermo lite is on and not the bag full indicator. The thermo detector is very reliable, but the bag fill valve often fails. If it is the thermo, check your hose and wand for blockage by dropping a coin through them,before opening the vac itself.Otherwise you may have a bad set of motor bearings causing the motor to overheat due to its age.
The 2100 and all its canister cousins made since 1982 seem to be prone to failure of the dial valve on top cracking internally. The causes the bag full indicator to come on and the vac to shut down.
To open the vac you will need to slide the locking keys and bumpers forward with the bag door open. Do this with a set of pliers. Once done the vac will open from front to back like a **** shell. Be careful to look at the underside hinge are of the bag door before separating and mark and locate the wiring harness . This vac only goes back together one way, perfectly assembled it pops together with ease. If any piece is out of line it`s like a RUBIKS Cube. Take your time . OEM parts are only available through an AERUS Elctrolux dealer or repair shop

Have you ever over the years replaced your brushroll ? Have you tried dropping a coin thru the hose from one end to see if it comes out the other end ? Have you taken the wand loose from the elbow ( the swivel part of your carpet sweeper) to see if there was a blockage ? Does the motor make a strange noise ? Have you ever had a tune-up on your vac.
You might think about taking your vac to your Aerus/Electrolux shop.
Joe

Call your local Aerus Electrolux office. If there is a problem in the electrical system you should get that checked before you continue with the machine. As for the cord replacement- Any Aerus service dept. can do that for you. I say an Aerus office because should you let a non-Electrolux employee work on it you will void your warranty.