Was trying to replace ink cartridge and the belt pulley came off. How do I fix it?

turn off your printer...then replace new cartidges.after replacing cartridge restart printer...always when you want to change or replace cartridge/Drum/fixing/belt trun off your printer...

There is a belt and two pulleys (one at each end) that _SHOULD_ be attached to the cradle.
If the motors that spin the pulleys have died, or if the belt is no longer attached to the cradle, then it's time to responsibly recycle the printer, and buy a new one; hopefully one that will use the same ink-cartridges.

There is a "belt" that has a pulley at each end, and the belt is connected to the print-head.

If you open the lid, you should hear the motor spinning the pulleys, and pulling the belt.
If not, then the motor is not functioning.

Check that the belt is still connected to the print-head -- if it has broken-away, it's time to replace the printer, because it's impossible to purchase a replacement part to replace the broken part.

If you have replaced your ink cartridge with a new one and are continuing to experience difficulties with print quality, please try cleaning and wicking the ink cartridge. If this fails to resolve the issue, the maintenance station may have an excess build-up of ink.
The maintenance station is located inside the printer on the right hand side. This is the same area where the cartridges sit when in the "idle" position. To access the maintenance station: Unplug the power supply from the back of your printer, open the front cover and look above the steel rod. You should see a conveyor belt with rubber teeth on it, like a fan-belt. On some models, the cartridge access will be very small, but the belt should still be visible. Take the top part of the belt and move it gently to the right.
***Note*** please do not pull outwards on the belt. The cartridges should come over towards the left side of the printer. The maintenance station will be on the right side, on the bottom of the printer behind the fixed cover. Clean the area with several damp cotton swabs or damp paper towels until the build up of ink is removed.
Once the maintenance station has been cleaned you should "wick" the cartridges. Remove the cartridges from the printer. Get a clean damp paper towel and lay it on a flat surface. Set the ink cartridge right side up, with the ink nozzles touching the towel and hold in this position for about 15 seconds. Then wipe the nozzles across in one direction only (left to right). Repeat this process, each time using a clean spot on the paper towel, until it looks clean. Dab the cartridge on a dry towel to make sure that the ink is flowing.
After you have wicked the cartridges place them back into the printer, securing them into the place. Plug the power supply back into the printer and close the cover. Next, click on "Start," "All Programs," "Lexmark series," "Lexmark Solution Center" and click on "Maintenance." Now, please click on "Install Cartridges." Select the cartridges part numbers and choose if they are "Old" or "New." Cancel the Alignment page. Then, click on "Clean to fix horizontal streaks" in "Lexmark Solution Center." The colors that you should see here are black, yellow, magenta (a reddish purple), and cyan (a dark sky blue). You should notice the diagonal lines above and below the solid horizontal lines. These diagonal lines should be solid from left to right with no gaps.
If there are gaps in the lines or the print diminishes across the page, you should run the "Clean Print Nozzle" page a couple more times to try and clear it up.

You need to remove the top cover to see where it goes, there's a spring loaded pulley on one side and a motor pulley on the far other side.

Please remove the cartridges from the printer. Take a dry lint free paper towel and gently wipe the contacts on the back of the cartridge (not the bottom from where ink is present). Wipe the contacts inside the printer (on cartridge carrier). Please try to print the self test page.

A technique to improve print quality is to try and clean the cartridge nozzles. You can clean the cartridge using the following steps given below:
Click on "Start," go to "All Programs," and down to the Lexmark. Click on the "Solution Center." Next, click on the "Maintenance" tab. Select "Clean to fix horizontal strips." This will produce a printed page.
The colors that you should see here are black, yellow, magenta (a reddish purple) and cyan (a dark sky blue). You should notice the diagonal lines above and below the solid horizontal lines. These diagonal lines should be solid from left to right with no gaps.
If there are gaps in the lines or the print diminishes across the page, you should run the "Clean to fix horizontal strips" page a couple more times to try and clear it up. If you still have gaps at the top and bottom, you should "wick" the cartridges by following the steps given below:
1. Please open the "Solution Center" again and go to the "Maintenance" Tab.
2. Select "Install color/black cartridge" and remove the cartridge (or cartridges) from the printer.
3. Get a damp paper towel.
4. Set the ink cartridge right side up on the damp paper towel so that the ink nozzles are against the towel and hold the cartridge in this position for about 15 seconds.
5. Now wipe the print head (on the bottom where the ink comes out) across in one direction only (left to right) until it looks clean.
6. Next dab the cartridge on the towel to make sure that the ink is flowing.
7. Snap the cartridges back into the printer.
8. On your computer, select "Old Cartridge install."
9. Repeat the "Clean to fix horizontal strips" one more time. If this fails to address the problem, the entire procedure may need repeating.
If you have replaced your ink cartridge with a new one and are continuing to experience difficulties with print quality, please try cleaning and wicking the ink cartridge. If this fails to resolve the issue, the maintenance station may have an excess build-up of ink.
The maintenance station is located inside the printer on the right hand side. This is the same area where the cartridges sit when in the "idle" position. To access the maintenance station: Unplug everything from the back of your printer, open the front cover and look above the steel rod. You should see a conveyor belt with rubber teeth on it, like a fanbelt. On some models, the cartridge access will be very small, but the belt should still be visible. Take the top part of the belt and move it gently to the right.
***Note*** please do not pull outwards on the belt. The cartridges should come over towards the left side of the printer. The maintenance station will be on the right side on the bottom of the printer behind the fixed cover. Clean the area with several damp cotton swabs or damp papertowels until the build up of ink is removed.
Once the maintenance station has been cleaned you should "wick" the cartridges. Remove the cartridge from the printer. Get a clean damp paper towel and lay it on a flat surface. Set the ink cartridge right side up, with the ink nozzles touching the towel and hold in this position for about 15 seconds. Then wipe the nozzles across in one direction only (left to right). Repeat this process, each time using a clean spot on the paper towel, until it looks clean. Dab the cartridge on a dry towel to make sure that the ink is flowing.
After you have wicked the cartridges place them back into the printer, securing them into place. Plug the power back into the printer. Close the cover and click on "Old Cartridge Installed" on the "Control Program" screen. Once the printer has reset, run the "Clean Print Nozzles" page twice. This should resolve the issue.


your's tech expert
Jeeth

clean the belt with a VERY SOFT cloth, there is a release lever to access the back of the belt. Replace magenta cartridge

That black thing is the drive belt for the print cartridges. It man have come off when you were playing with the cartridges, or you may have a broken part that let the belt drop. Unless you are familiar with printer repair you do not want to open the unit and try to fix it. Take it in to a shop for repair...or you may create more problems than you fix.
However if you want to try use this site to get a guide on howto:
http://www.pdfoo.com/pdf-217/printer.html

There should be a small pulley sticking out somewhere deep inside.  But you'll probably have to disassemble the printer in order to get at it.  PITA.

you need a replacement belt as any repairs to the belt will not withstand use, you may be able to order this part online