Network connectivity problems

I have been having a strange issue with my laptop (dell inspiron 8500/windows xp home). whether i am using a wireless connection or an ethernet cable, if i leave the computer alone for an hour or so, it will no longer connect to the internet. if i open up my network connections, it says that i am still connected, but to actually get on the internet i need to restart my computer. i am using the same router for 3 computers, and this is the only one that seems to be having a problem. please help me with any thoughts or suggestion as i have been wasting far too much time trying to figure this out without having much luck. thanks a lot, dave.

click Start> Control Panel> right Click on Network Connections> click Open> right Click network connection> Properties> click Configur> Power Managment> uncheck Allow computer to shut off this device

i disabled the power management on both the wirless and local area connection, but to no avail. i'm still having the same problem. any other suggestions?

Only other thing I can think of is to look at the Power Options in Control Panel