I can connect wirelessly to the internet, just not through my Own Network

Im sharing a house with two friends and we have our own wireless network set-up. I'm having trouble connecting to our network. It happened after I updated something and my computer restarted. Before it restarted I was on my network, and when it finished restarting it tells me I can't connect. It has happened twice and I have no idea how I fixed it the first time. But my wireless is on, and my network is working because my friend is online right now. I'm not sure how to get back onto the connection without it telling me there is a problem with the connection when obviously there isn't.

 

What did you update?

If you are using Windows XP, there is a "restore" function

Start->Programs->Accessories->System Tools-> System Restore