more accurate information required
I presume by "modem" you mean an ADSL wireless modem router running on the "N" protocol with the 300mb/s dual band?
Assuming thats correct
1) which two bands have you set the channels to?
2) is the printer running on G or N protocols? Presumably the printer is only capable of single band?
3) is the computer running on B,G or N? Is the computer capable of dual band?