Right side no yellow ink
You can get the manuals for the 3100cn printer from the Dell support website (http://support.dell.com/support/edocs/systems/3100cn/en/index.htm). They include some troubleshooting steps for determining what is causing a number of different problems with the printer.
Did you make sure there was nothing blocking the toner on that side of the toner cartridges you replaced?
If you haven't already tried it, I would also suggest cleaning the printer to see if that fixes the print problems you are seeing. The User's Guide (in the link above) has a section describing how to do this.
If that doesn't fix things, run the tests for print quality and contact Dell support (contact information is in the manual, or on the Dell.com website).
Hopefully this will help you get the problem fixed if you haven't already done so.
Dell Customer Advocate