What model do you have? I have a XPS400 and 1&3 is a memory error.
Just google dell diagnostic lights with the model number and it should tell you the codes. I have a Dell XPS 400 and When I searched for the lights I found it in the troubleshooting documentation.
Here is the link for the XPS 400. http://support.dell.com/support/edocs/systems/xps400/sm/adtshoot.htm#wp1054184
Dell may use the same codes for all computer But I am not sure.
Hope this helps