Get all the easy stuff out of the way first:
Test your memory with memtest
Test your hard-drive with the manufacturer's utility
Install pfSense 2.0 Release, it's been out for a while now (do your config from scratch for best results and do not install ANY packages)
Make sure your hardware (especially your nic cards) are on the freebsd compatibility list
You either will need to swap out your production machine for this, or do the work after hours. Once you have done everything above, come back and let us know how it goes.