When it freezes, whats the longest amount of time you've left it alone?
Quick Fix #1:
So lets break this down... SSD won't boot on Mobo1. SSD will boot on Mobo2 (Exact same model). Mobo1 will boot other drives just fine. And lastly, you have 30+ computers to work with. My thoughts would be to just permanently swap the Mobo of two computers here, and see if they can work well.
More troubleshooting ideas:
A: Try booting with a different SATA port. Looks like that mobo has 4 ports to choose from.
B: Disable/Stop any third party programs that may interrupt Windows Startup process. Use MSCONFIG to turn programs on or off. It could be a network issue, where a startup program like Skype (Bad example I know.) wants to access the network, but cannot find any network connection. So the computer hangs and waits.
C: Use Windows last known good configuration:
http://pcsupport.about.com/od/windows7/ss/last-known-good-configuration-windows-7.htm
D: It wouldn't hurt to do a few cleanup or scanning checks in Windows 7 on the SSD that freezes on startup. First get it to boot on another motherboard. Then:
D1. Goto My Computer and right-click the Local Disk (C: )
D2a. Under General tab, click the Disk Cleanup button, and run the cleanup process.
D2b. Under Tools tab, click the Check-now button, for an error-checking scan.
E: Uninstall any recent Windows Updates:
http://windows.microsoft.com/en-us/windows/remove-update#1TC=windows-7
F: Lastly, Reinstall Windows. - I would transfer the documents to a third drive and perform a fresh installation of Windows 7 over it. Don't transfer back the files yet, and see if it will bootup again on the original motherboard. Hopefully that would get rid of any startup issues or possibly missing or corrupt files/sectors.
Hope this helps.