websites not showing up on web browser

ok i'm really worried. i just bought a macbook today and loaded some applications and updated the software. i went to go on firefox to browse some websites and youtube doesn't work and some other random sites. i double checked by using safari to visit the same websites. they don't work either. i went to another computer and went on youtube and other sites and they work fine. most websites work but some like youtube dont' work. macbook seems to think that it can't connect to that website like it never existed. any help to a new macbook user would be greatly appreciated! thanks

You may need the Flash plug-in. Check here. If there is no animation, you can download it and Shockwave's from there.

The Mac plays Windows Media files through the Flip4Mac plug-in, available at versiontracker.com or macupdate.com. It won't help with DRM'd meda files, though.

While at version.com or macupdat.com, download the Perian extension for QuickTime to gain more codecs. It's ReadMe should tell you where to drag it.

i don't think thats the problem

i think i have flash because google video works fine. i checked and i have java and flash installed. whenever i visit some sites this is what i get:
Safari can’t connect to the server.

Safari can’t open the page “http://www.youtube.com/” because it could not connect to the server “www.youtube.com”.

this happens with several other websites for example i was trying to visit the parallels program website and for me it has the same error message as it had for the youtube. but other websites work fine...i'm really worried.

stupid me

wow i'm so stupid. i thought my macbook was broken, but it was actually peerguardian. i thought when i press quit on peerguardian it would go away but it was still running in the background somehow so i uninstalled it and i can visit all sites now. haha....wow...thanks for all the help anyways