Try this- using a wired connection go into the router settings and click the Wireless settings link. Opposite 'Mode' use the drop down box to change it to 'g only'. Now go to the Channel numbers and change the channel to No. 13. If this does not work, go down through the channels until you find one that does.
If you have any thick or foil insulated walls between the PC and the router the reception can be greatly reduced. A wired connection will always be faster and more stable than wireless, so especially if you are a gamer, use an ethernet connection wherever possible. Many use a Homeplug network, which is faster and more stable than wireless,
HomePlug AV | Broadbandbuyer.co.uk