have u tried to put the router in a proper location../ ensure if you have kept your router atleast around the middle of part of your building and more it should in open place which place is atleast near../ generaly, home wireless work good within 100/200 meters of radius../
As per my experience of 7 DBI indoor D-Link Omni antenna doesn't make any sense if you have installed your router in a corner../
BTW, what is the distance of your PC and Router..? Well, rather then purchasing Antenna for indoor, try for NetGear it has excellent range with it's built in rubber antenna../ Antenna are expensive then wireless../
Rgds,
Dhiren