Enable WPA, and to show SSID.
Next, on the PC, open a command prompt and type:
ipconfig /release
Then:
ipconfig /renew
I'm assuming you're using XP since you didn't say. Vista or W98 may be different.
About a month ago I bought an Ativa G-Wirless Router, and mostly of the time it work fine, but somtimes, it stop receiving packets, but sending packets. I have the options checked in "Obtain an IP address automatically" and "Obtain DNS server address automatically". I belive, since that is what Live Messenger tell me, is than the problems are Host, DNS and Key Ports. What can I do?

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic