My lexmark x3650 printer will print, but the pages come out blank. did a test to see if there was no ink and the diagnostic said 40% ink is still in there.

Regarding the Lex1 cartridge's no printing/severe fade (or similar) during printing, my answers are provided below:

For the poor print quality problem (degraded image quality) you are observing, we suggest you first visit the "Print Quality" page of the "General Information" section of the Inkjet 411 website and follow the suggestions provided: http://inkjet411.com/?page_id=1432

A. 1. Cartridge & Printer maintenance should also be evaluated - ensure both ink cartridges and flexible driver contact cables (where the cartridge interfaces to the carriage inside the printer) are thoroughly clean: http://inkjet411.com/?page_id=1519

A.2. Perform a hot-water flush on the suspect ink cartridge, refer to video procedure here: http://inkjet411.com/?page_id=1519

A.3. Run a quick test print to evaluate cartridge performance (i.e. 4-color test print):
http://inkjet411.com/?page_id=146

For information on North American ink refill services (for Lexmark 1, 2 and 3 ink cartridges) at a major retailer near you (should you wish to save ~50% on ink costs), general printing problem resolutions or advanced Lexmark printer diagnosis procedures (advanced cartridge diagnostic tests/cartridge error bypass & printer reset methods, etc.), please visit Inkjet411: http://www.inkjet411.com

Try to re-seat the cartridges in the printer. Open the printer cover > remove the cartridges > close the printer cover > re-brick you printer by pulling out the power supply - black box behind the printer where the power cord is plugged in, and re-plug after 10 seconds. When the printer turns on, reinsert the cartridges and close the cover. Try to print a document again to verify that the problem is fixed.

If that doesn't help, the problem could be due to a clogged print cartridge nozzle. Please follow the steps below to fix print quality issues with your model:

1. On your computer, go to Start menu.
2. Go to Programs.
3. Go to Lexmark 3600 Series folder.
4. Select Lexmark Solution Center.

From the Maintenance tab, select Clean to fix horizontal streaks. Your printer will then print a page forcing ink through to clean the print cartridge nozzles.

After printing the test page, try to print a document again to verify that the problem is fixed.

You can try to manually wipe the cartridge nozzles with a moistened soft cloth to clean it from dirts and clogs. You can also clean the nozzles using the Lexmark software on your computer. If you're using Windows, go to Programs/All Programs > Lexmark 3600-4600 Series folder > From the printer folder, click Maintenance > Clean Cartridges > Print. A page prints, forcing ink through the print cartridge nozzles to clean them.

Access the manufacturer's web-site: http://support.lexmark.com
and do a search for 'X3650'. Choose the device-drivers for Windows 7.
Download. Install. Print a test-page.

tried re-installing the sortware or going into printer diagnostics in the start,control panel.
and it will run a diagnostic & try to print a test page, & clean the cartriges.
If not the printer's broke
Hope this help's

all in one guide

http://cluetechnologies.com/index.php?topic=687.0

Download and install the latest driver, making sure that it is for the version of windows that you are using. 
http://search.lexmark.com/printer/US/en/16F1200

You can lastly try a hard reset of the printer but if that is to no avail the printer has an issue with it. See if you can get it to work with another computer for the heck of it just to make sure.

Try checking the ink cartridges and make sure they have ink in them or it will keep printing blank pages. Then try printing a test page by going to control panel, clicking on printers and faxes and right clicking on your printer and going to properties. Then go all the way down to the bottom of the page and click print test page. It will clean the printer cartridges and align them to print correctly. It should work after that.

I have a z600 that i use. If not used for about a month the ink does clog the print nozzles and eventually ink cartridge does dry out. To avoid this even if i dont have to print anything I run a diagnostics test that prints out a nozzle aligment test every two weeks.The great thing about this is that it uses very little ink.You can find this test in your software that was provided by Lexmark. This will keep your nozzles cleaned and you will notice this helps extend the life of your cartridge.