My dell is saying to close paper cover - Dell 3100cn Laser Printer

Sounds like the sensor for the cover is not working. If you open the cover when it is on, then close it, does the error remain? It only needs a microscopic amount between 'open' and 'closed' - check if there could be a tiny bit of paper somewhere around the edges.
Failing that, get in touch with Canon.

Here are the things that a steady red light may indicate (from the Owner's Manual):

• A paper jam has occurred. To solve the problem, see "Clearing Jams in the Paper Tray". • The front cover is open. Close the front cover. • The top cover is open. Close the top cover. • The paper tray is empty. Load paper in the tray. See "Loading Paper". • A toner cartridge is not installed. Install a toner cartridge. See "Installing the Starter Toner Cartridge".
• A paper jam has occurred. Check the paper tray area.
• The front cover is open. Close the front cover.
• The top cover is open. Close the top cover.
• The paper tray is empty. Load paper in the tray.
• A toner cartridge is not installed. Install a toner cartridge.

After a paper jam occurs in the rear cover of a Dell Laser Multi-Function Printer 1815N, the printer will not resume when the jammed paper is removed. This is the normal behavior of the printer as there is no sensor on the rear cover of this printer.

To open the back cover and remove any stuck paper, perform the following steps:

1. Open and close the front cover.
   The jammed paper may automatically exit the printer. If the paper does not exit, go to the next step.
2. Gently pull the paper out of the output tray.
3. If you cannot see the paper in the output tray or the paper does not move when pulled, open the rear cover.
4. Skip to step 9. If you do not see the paper, go to the next step.If you see the jammed paper, push the two blue pressure levers up and remove the paper.
   
5. Release the blue strap, the rear cover stopper, and fully open the rear cover.
6. Unfold the duplex guide fully.
7. While pushing the fuser lever to the right, open the fuser door. NOTICE: Make sure to unfold the duplex guide before opening the fuser door, or the fuser door may be damaged.
   
8. Pull the jammed paper out.
9. Return the levers, fuser door, rear cover stopper, and duplex guide to their original position.
10. Close the rear cover.
11. Open and close the front cover.
    Printing automatically resumes.

The Paper Cover is located on the top of the printer. It is the vented panel just behind where your printed documents come out. It lifts up to clear paper jams, and documents won't print until it is closed. Just push the panel down until it clicks in place...that should do it!

Dell 3000cn Color Laser has a duplex. If you face the printer on the top right of the duplex there is a button to release the duplex and it folds back. The reg cover is a door on the back of the printer that is covered by the duplex, try opening again, I know you have done this, maybe even wiggle it a little see if it registers as closed.

Also check to see if any dust or paper pieces maybe be jammed in there.

Don't take risk about your equipments. consult a enjineer.

close the back door of the paper tray 1. the paper tray for this printer actually has a "door" that opens up. silly but true

Please double check if all doors, including the paper tray cover, are firmly (repeat FIRMLY !) closed. Seemingly all such are designed as precautionary measures for safe operation.

Push the side button and open the front cover

Pull out the jammed paper from the duplexer. If jammed paper cannot be found, go to the next step.

Pull up on the belt release levers and rotate the belt unit up

Remove the jammed paper and close the belt unit

Close the front cover

After researching the error online, I solved my problem by simply pushing the back cover of the unit closed; I didn't even know it had come open after I removed my jam.

Hope this helps!

http://support.dell.com/support/edocs/systems/3100cn/en/UG/section20.html#638412