If what
BOAC says doesn't help then:
Shut down the PC, switch off the router and leave for a minute or so while you pour a strong drink, once the router has fully re-initialised switch on the PC and get it to connect and then down load a Wi-Fi sniffer program such as
netsurveyor and see what other channels might be interfering with yours, Ideally you need at least 2 free channels either side of yours. Change the channel on your router to suit.
Caution if you download from
C-NET you will end up with tool-bars and other crap you didn't want.