15dbi omni antenna setup to linksys wrt54gl

i am looking for help, if anyone of you ca help me with my situation i will give you or donate to you some money just help me configure my wireless network, i have been trying for two days now and still i can't get my 15dbi antenna and my linksys wrt54gl to work, i am using dd-wrt system and what now should i do so that i can lengthen the radius of my wireless connection, i tested the signal of my linksys router and it transmit up to 20 meters outside my house then i attached my 15dbi omni antenna so that i can stretch it to 800meters but the connection is still the same, so i am now stuck and don't know what to do, please help me out

Be sure to assign the TX and RX antenna to the side that your 15dB antenna pigtail is connected on, under Wireless-Advanced wireless setup and while you are there push the Xmit power up to 84mW. Hope this helps.