How can i clean heads on hp 6540 under windows 7? The printing has faint colors

It could be the "clean print head" sponges. The area under where the print head sits is where the ink go during the head cleaning cycle. They can become saturated with ink and smear onto the print head and then onto the paper.

Does this link to an hp.com troubleshooting page help you at all? It addresses the failure to print a color.

http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00219782&tmp_task=solveCategory&cc=us&dlc=en&lang=en&lc=en&product=357211

Good luck to you!

Your Printer head need cleaning, try doing a self cleaning or change you ink, hope this helps.

2 possible causes: 1 - the ink has started to dry in the cartridges, it has become too thick for the heads to project on the paper correctly and in the end it has clogged the printing heads - replace the cartridges and run several deep cleaning cycles. 2 - hardware fault: either the data cable (the ribbon that connects the print head carrier to the mainboard) has been damaged and it will have to be replaced at a repair shop or the processor of the printer has just failed - this is terminal since it will be cheaper to buy a new one than to replace the mainboard. To make a pretty exact diagnose of the situation take out the cartridges and see if the printer recognizes the situation when you try to print something. If you get an error message then it's the data cable, if the printer is unresponsive then it's the processor - time for a new one.

I believe you have to clean the heads of the printer by going into your printer properties from your computer.

HP doesnt have a software set available for you printer and windows 7 the link below explains it right from HP
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c01874792&lc=en&dlc=en&cc=us&product=357211〈=en

Finally - continued to do further print head cleaning (about 6 times, included 2nd level) and finally started printing black again.

Your post "...it prints very faint horizontal lines in color..." is indicative that indeed your color printheads are clogged and would need repetitive deep head cleaning. This is of course would require that you keep on cleaning until such time as the faint color lines have turned to legible print.

The color cartridge sping was loose. I am in the process of super gluing it into place. Hopefully it will work.

You could try doing an alignment which i think is a maintenance option on this machine. You should find it in the driver options. You could also look at my previous posts about under head cleaning. Look here -> http://www.fixya.com/support/t137335-problem_print_outs_from_printer