Print is unreadable, low resolution and washy - how can I get a better print quality?

System: windows 7, PDF Archt. 2.0, Printer DELL 3100cn PS.
When printing, the quality is very low, and unreadable (in b/w and in colour) - If I change the printer setting (print mode) from "normal" to "high quality" there is no change in quality. Can anybody help me?