The printer is not printing all letters clearly. I want to clean the printing heads to see if this will help.

From Canon Help Files.

Automatic Print Head alignment failed
Possible causes are as follows:
A4 or Letter-sized paper is not loaded on the Auto Sheet Feeder.
Press the RESUME/CANCEL button on the printer to clear the error, then load one sheet of A4 or Letter-sized paper in the Auto Sheet Feeder.
Automatic print head alignment cannot be performed using paper from the Cassette. For automatic print head alignment, always load paper in the Auto Sheet Feeder.

Print Head nozzles are clogged.
Press the RESUME/CANCEL button on the printer to clear the error, and then print out the nozzle check pattern to examine the print head condition.

For information on how to print a nozzle check pattern, see "Printing the Nozzle Check Pattern."

The Paper Output Slot has been exposed to a strong light source preventing correct Print Head alignment.
Press the RESUME/CANCEL button to clear the error and move the printer to a darker location.
After carrying out the above measures, if the problem continues after aligning the Print Head again, press the RESUME/CANCEL button to clear the error, and then perform manual print head alignment. For details on manual print head alignment, see "Manual Print Head Alignment."

Inkjet printers need to be used frequently to prevent ink drying out and blocking the print head nozzles.
If the print head cleaning maintenance routine does not clear the blockages, then print head needs replacing, but it may be expensive.
It may be more cost effective to buy a later model and better printer than replace the print head.

take out the colors and see if the black prints. if not you could need a new one.

go into setup and try printing a test page, if this prints, the printer is ok and the source of your print is at fault. as for the missing letters and etc, it sounds like you are out of ink or the print head is dirty, try cleaning the head (the software that came with your printer allows you to clean the heads, but be aware this takes lots of ink to accomplish.

If you have clean the print head and nothing,you need to replace the print head.

You need to clean the printer heads. Go to start-->control panel-->printers. Right click on the printer and select properties. Click printing preferences at the bottom and goto maintenance tab. From their you can choose to do a "head cleaning". You may have to run it a few times and print a "nozzle check" each time to see if it's any better. If it's not perfect after 3-4 times wait a day and try again.

1. Shake ink cartriage and Re-clean the print head, dripping alcohol to drain off and wipe clean w/tissue (do not touch with fingers).
2. Apply slight suction to print head to clear clogged ink (if by mouth, spit out ink and water rinse etc.).
3. Re-clean per step 1
4. Insert ink cartiriage, seating it all the way into holder.
5. Run a "cleaner sheet" through printer to clean al printing parts
("cleaner sheets" are available at office supply stores).
6. Printer should print all parts of letters.

This usually indicates a need for a new print cartridge or the printer head is dirty. You can run the automatic printer cleaning utilities. Note: do them several times.
Also, if you are a little handy, use Qtips and rubbing alcohol and clean the print head.

Open the cover over the print head and *carefully* inspect the clear thin plastic strip that runs from left to right near the print head. If you see any lubricant (white grease) on this encoder strip, it needs to be cleaned off.
1. With the cover open and the print head in the center, unplug the power cord. This will allow you to gently move the print head left or right.
2. With a cotton swab wetted with rubbing alcohol, *gently* wipe the grease spots from the encoder strip. (Be VERY CAREFUL you don't dislodge the strip.) You may need to move the print head to the left or right to get all areas cleaned.
3. Let the alcohol dry off completely. With the area clear of cleaning tools, debris, and fingers, plug the power back in.
4. Try a test print.

Solution: Perform the print head cleaning procedure MP750 / MP780

Print Head Cleaning / Head Refreshing If the printed Nozzle Check Pattern is broken, missing, or a specific color is not printed, clean the print head.

1. Press the <Menu> button on the printers operation panel repeatedly until [MAINTENANCE] appears in the LCD.
   
   
2. Press the left [<] or right [>] arrow buttons to select the cleaning setting you want. Select [HEAD CLEANING] or [HEAD REFRESHING] for deep print head cleaning.
   
   Note: [HEAD REFRESHING] uses more ink than [HEAD CLEANING], so perform [HEAD REFRESHING] only when necessary.
   
   
3. Press the <OK> button.
   
   
4. Print a Nozzle Check Pattern and perform at least two Head Refreshings if the pattern is not correct.
   

Now if you mean not printing the letters correctly go to this site and download the drivers and reinstall them. Also you will find manuals on HOW TO sort of thing:
http://www.usa.canon.com/consumer/controller?act=ModelInfoAct&tabact=SupportDetailTabAct&fcategoryid=238&modelid=10444#DownloadDetailAct

hope this helped, please leave rating