My new netbook wont connect to my wireless internet?

I just got a new asos netbook for my birthday and i cont connet it to my 2wire router wirelessly. If i connect it with an ethernet cord it will go online but if i try to do it wirelessly, it says it cant connect. i tried changing settings around and i have tried connecting to somebody elses wireless and i was able to connect to theirs. anyone with an idea please help.