Internet does not respond after inactivity

[JurasicJet]

Hello:

The problem starts when you do not use the computer for a while (maybe half an hour to an hour). When you open the browser and attempt to contact an internet site, the site does not respond. It comes up with a window that says "www.Yoursight.Com could not be found. Please check the name and try again".
The wierd thing is that if you click on multiple bookmarks in fairly fast order (only giving each on a few seconds) then sometimes it will work. Otherwise, you must shut the computer down and restart it.
I have DSL. Westell WireSpeed modem hooked to a D-Link DI-525 router. The wireless part of the router is turned off and I just have my two home computers hooked into the DI-524 with LAN cable (I didn't need the wireless part of the router but wireless routers are cheaper than non-wireless routers - go figure). Both computers have on-board LAN and I know one has a Nvidia chipset. Not sure what the other one has. Oh, by the way, both computers suffer from this problem.

THanks

[Sterling_Aug]

Click Start/settings/control panel/system/device manager/select the network card in question. Right click on the card/properties/power management tab/uncheck for this device to turn off and save power.

[JurasicJet]

I have previously unchecked the power save mode of this controller with no apparent affect, it still "locks up" when not in use.
What about "wakeOnLan from Power Off", should that be enabled or disabled? It is currently enabled.
Could it be the wireless router?

[dip switch]

Also (if you have PPPoE) set the modem to always connected not connect on demand. The westell is a modem/ router you might want to use a switch instead of the d-link to hook your computers.