Browsing internet cuts wirless connection

[pthomas]

I have searched the internet and cannot find problem similar to mine.
I have a HP pavilion 9700 laptop with wireless connection and a desktop with cable connection.
I can connect to my wireless network and if I don't use the internet then I can stay connected until i decide to disconnect. This may be days and days connected.
However when I use the internet and surf a lot (watch streaming videos, visit many sites etc then the connection drops off. I can see my SSID in the available networks with "excellent" strength but I cannot connect. The only way to connect again is to reboot the modem. It all works fine if I use cables but internet usage over wireless cuts the connection.
I know I am using my own SSID and it is set up with 64 bit WEP encryption.
I have the encyrption keys set up on the modem and the laptop.
It can't be interference as it only gets cut with internet usage (if i just have a page loaded and forget to close down internet i can stay connected overnight. It just seems the connection may get overloaded and shuts off but I don't know)
thanks
phil