Wifi connection goes down after 30min

Evening Folks,

Got a computer here with XP SP2 and a WMP54G wifi card.

The computer did have a asus wifi card in it for a few months but one
day that card stopped working. It could see the network, but wouldnt
connect.

So anyway threw that away and put in a linksys wmp54g v1. This worked,
and I just pointed windows at the driver so i didnt get all the
bloatware and I use the windows wireless zero config wizard - all
good, but I did have to uninstall the asus wifi software.

For some reason though after about 30min of use the connection drops
and I cant ping the router???? Although it shows as connected.

What would casue this????

-Al

And a repair doesnt fix either