ATV 2 Unable to Sign In iTunes

Hi Everyone,
I just got my new ATV 2 and can´t sign in iTunes for the Home Sharing. I have access to the internet because the ATV 2 updated to 4.2.1 and I can listen to Internet Radio Stations, watch movie trailers and browse Flickr but don´t have access to Youtube, Mobileme, Home Sharing and can´t set Time and Date either in the other hand Airplay works flawlessly.
Following an advice I check the Apple Time and Date server update in the Mac and works perfectly.
I use a MBP unibody with 10.6.7 and iTunes 10.2.1.
Please I need HELP!!!! it´s the first time an apple product fails on me and will really appreciate any suggestions.
Thanks,
Jose

MBP 15 2.4 Mhz 4 Gb 250 Gb HDD
MBA 11 1.6 Mhz 4 Gb 128 Gb HDD
iPad 1st Gen 32 Gb Wi Fi
iPhone 4 32 Gb

Have you turned on Home Sharing within iTunes on the Mac? Double-check the sign-in names and passwords (CAPS matter) for the other services as well.

Also, you may just need to reset the ATV2 - I had to do that to mine this week to get it to see Netflix again. You can either unplug it from the power for a minute or so or hold the bottom two buttons (I think) on the remote to force it to power cycle.

Make sure all ports on your network are open. Apparently the ATV uses some odd ports that may need to be opened.