1) You did not mention the Qt filter. You might check to see if you have the Qt filter set the same on both radios. This is an additional layer of privacy featured on this radio.
2) Verify you have good working batteries. A bad battery or uncharged battery can cause a no transmit situation.
3) If these do not work, reset your radio back to a basic operation by shutting of the code, Qt filter, call tone, weather alert, Vox/iVox, roger beep, etc. At this point your radio would be operating just on a simple frequency. See if you can communicate with all these special features turned off. If so, slowly add back in the features you desire.
4) If your radios still fails to work and is less than one year old, call the 800 number on the pamphlet, have your serial numbers and radios handy. Your radio if not physically or water damaged is possibly still under warranty.
Most of the time when a set of radios has your problem description, it is the Qt filter, or possible improper use of a special feature such as call tones or iVox. These would be the first things to check.
Here is a link to the user guide: http://www.giantintl.com/ContentManage/manuals/Moto/T8500%20English%20only%20June5.pdf