Connected to wireless network, but no activity

Hi All,

Would greatly appreciate any help with the following problem. I've been using a friend's old laptop running Windows XP Sp 3, and using a RaLink RT2500 Wireless LAN card to connect to wireless networks and then to the internet. The networks I'm connecting to I have no access to edit.
This has been working just fine (if slow) for the last 2 months or so, when a few days ago the laptop would connect quickly to the wireless network, but there is no activity, i.e. packets receieved hardly moves and packets sent goes up very slowly. Signal strength and link quality are fine, but its really not working.

Any suggestions how to fix this would be greatly appreciated. I've tried this on 2 networks and the problem persists. Could it be hardware? Would another network card do the trick?

Thanks!
Richard