It's possible and highly likely the Apple TV requires a HD resolution. The 225MW is
1680 x 1050 which is not a HD resolution. You could try setting the Apple TV to 720p on another display first.
I have an old Samsung SyncMaster 225MW which I am trying to connect an old apple tv with xbmc via the hdmi port. I get the message "no signal" when I remove the cable it changes the message to "check cable", The ext in port works perfectly for both audio and picture. I have checked the hdmi cable and apple tv on another tv and they work perfectly- any suggestions?