I can't find where to connect the USB cable in the printer

1. Confirm the USB port on the computer you are connecting your printer to is being recognized by your computer. The easiest way to do this would be to plug a known good USB Memory stick into the USB port you want to use. If you can read the contents of the USB Memory stick then the port should work. Remove the Memory stick, start the printer installation program (Make sure you don't the printer connected), want until the setup program tells you to connect the printer before you attach the Printer's USB cable.
If the printer isn't recognized try a different USB port, when picking a new USB port to try select a higher priority port, for example in increasing priority from, an external USB hub, a powered external hub, a monitor based hub, USB ports on the front of the computer, up to the USB ports at the computer rear. For USB ports on the same circuit select an USB 2.0 before an USB 3.0 port

Hello, you could opt for the USB connection. Plug one end of the cable into the USB port on your computer. After, plug in the power cable and turn on the printer.

Check the type of connection - are you using a USB connection or a Wireless connection?
- If USB, turn off the printer. - remove the power cable at the back of the printer, then remove the cable to the wall outlet. Wait for 10 sec. then reconnect all cables. - turn on the printer and check if the computer detects the printer. - If not, try to remove the USB cable at the back of the printer and computer. Wait for 5sec. reconnect the cable back. Try other USB port if not detected. - If still not detected try to use another working USB cable. - If replacing the cable did not resolve the issue, try to install the driver of the printer.
- If wireless connection try to check if the printer is connected to your router. Run the Wireless Setup Wizard in the front panel of the printer. Select the name of your router. - Download the Network Diagnostic Utility on the HP.com website to check what is causing the issue. It will give you the instruction on how to resolve the problem.

You need a Printer usb cable. It is now common that company don't offer the cable with new printer. You can use an old one or buy a new.

• Connect the USB cable directly to a USB port on the computer
• Connect the USB interface cable
• Delete the printer (MacOS X), and then add it back again
• Disconnect and reconnect the USB cable to ensure a secure connection
• Reset the printer
• Try a different data cable
• Verify proper driver installation in Mac OS X

• Connect the USB cable directly to a USB port on the computer
• Connect the USB interface cable
• Delete the printer (MacOS X), and then add it back again
• Disconnect and reconnect the USB cable to ensure a secure connection
• Reset the printer
• Try a different data cable
• Verify proper driver installation in Mac OS X

Hello,

They do make adater cables for such problems. Here is just one such example: Parallel to USB Cable

Make sure you get the correct 25 pin cable. They have this type also:

Parallel to USB Cable 2

You can search the web for more companies. Google parallel to usb printer cable.

After saying all that and checking your printer info, I see that the 840c has both a parallel and a USB cable port. See page 21 of the manual: HP 840c Manual

If you go that route, you will need a standard USB cable. The shorter the better, but no longer than a 6' cable. Make sure you follow the iinstallation instructions for the USB setup in the manual.

Thanks for using Fixya.

Hello !

Give this a try;

Go to Printers and Faxes and delete your printer icon.

Disconnect the USB cable.

Restart your computer.

Reconnect the USB to your computer.

Your computer should see your printer. If it does not, move the USB cable to another port on your computer. It's also possible that your USB cable is faulty - replace the cable.

Install the printer driver.

Hope that helps.

If you go to the Canon support site here you can downlod easy setup instructions. This page has some other manuals and user guides that may also be of use.
Here are the basic usb cable instructions:
Connect the USB Cable Correctly (i70 / i80 / iP90) Instructions to connect the USB Cable Correctly to the printer (i70 / i80 / iP90). Before connecting the cable
After confirming the printer and computer are turned off, connect them using the USB cable (sold separately).

Note: Below is an example of what a standard 'A to B' USB Cable looks like.






How to connect the USB cable

• Plug the flat connector of the cable into the USB port of the computer.
  
  Note: If there are two or more USB ports in the computer, any available port may be used.
  
  
• Plug the squarish connector of the cable into the USB cable receptacle of the printer.
  
  

<1> Computer's USB Port
<2> Printer's USB Cable Receptacle



I hope this information allows you to resolve this issue. If you need further assistance, please post back with a comment to this thread.
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the printer is designed to work with a parallel cabel connection. usb to parallel conversion cables may or may not work. 
now for the second part is, about the driver (visit manufacturers website for updated drivers), usb driver behaves differently compared to parallel drivers as it expects a usb printer connected to a computer. try both drivers. remember, it may or may not work.