are your walls made of metal that will kill your wireless, i would assume if you have a cellphone and you can get signal outside and not inside its your house.
i had a bad signal when i placed my router near my modem, move it to a high point away from other electronics and power adapters as they tend to put off internference.
also its best to not have a 2.4ghz cordless phone as it is on the same spectrum of your router.
also make sure you put the antennas like it shows in the dlink quickstart booklet