I have a Xerox DocuPrint M75 Printer
Why does my printer print only in red?...They are brand new cartridges!

Presume you?ve done all the standard things, like head cleaning and
trying another printer just to make sure it?s not software failure. As
far as I recall, the print heads on this model are not incorporated in
the replaceable cartridge. Head failure on older machines is not
uncommon and this may be the cause, in which case I?m afraid it?s a
bucket job. Not even the most experienced techy can repair some head
failures because ink migrates into the delicate circuits.

If you?d be satisfied with black only, perhaps fill the red cartridge
with black ink and change all text to red to fool the printer.

Sorry not to be more encouraging.

Best

I have not been able to locate any information about the Xerox
DocuPrint M75 printer, but did find some information pertaining to the
DocuPrint M750.  Everything here applies to the M750, so if this is
not the correct model, this may not help you.

Try to isolate the problem to the printer by printing an internal test
page.  "Print a test print by pressing and holding the Resume button
for
more than two seconds. If the test print is good, the problem is
most likely not with the printer."

If the test print is successful (prints all colors), then the problem
is NOT with the printer.  Delete the printer driver, re-download the
correct driver for your operating system, and install the new driver. 
Drivers for your printer can be found here:
http://www.support.xerox.com/go/results.asp?Xlang=en_US&XCntry=USA&prodID=M750&ripId=&Xtype=download

If installing a new driver does not fix the problem, you will likely
need a new printer cable.  "If not using a USB cable, the printer
cable type should be IEEE std 1284 - 1994 compliant."  I believe all
new printer cables currently meet this requirement.

If the test print exhibits the same problems as before, try to clean
the printhead(s) as follows:  "The clean function is used to restore
the print head when the nozzles become dirty or clogged with dried
ink.
Open the Maintenance tab by selecting:
- Start > Settings > Printers. Select the DocuPrint M750/M760 icon.
- Select Printer > Properties. Select the Paper/Output tab and click
on the Status button, then select the Maintenance tab.
- Select Clean? to display the Clean Print Head window.
- Select the black print head, color print head, or both, depending on
which you want to clean.
When you select Clean, the printer cleans the selected print head(s).
This button is disabled if neither head is checked."
This procedue may need to be repeated up to 3 times to restore full print quality.

If the automatic cleaning cycle does not fix the problem, try manually
cleaning the printheads:
"Remove the print heads and clean with a damp cloth. Use
a clean cloth, dampened only with water, to gently clean the
nozzles (the copper-colored area on the bottom of the print
head). When cleaning the color print heads, wipe the nozzles in
only one direction so that the colors do not mix."
(Xerox officially says to use water, but I have also heard of using
ispropyl alcohol.  If you choose to try cleaning with isopropyl
alcohol as a last resort, you do so at your own risk.)

All information was obtained from the Xerox DocuPrint 750 Quick
Reference Guide, which was downloaded from the Xerox website.
http://www.xerox.com/downloads/usa/en/q/Qrefguide.pdf

If your printer is still not working, you should consider investing in
a new unit.  The cost of repair (if even possible) will very likely
exceed the replacment cost.

Best of luck.