Andy, first of all we need to find out what is causing you system to freeze. How long ago did you start getting this behavior? Which is the current BIOS version of your unit? The Intel motherboard D975xbx2 has been out of support since December 2009, so the latest BIOS version available is 2838.
I recommend you to disconnect all hard drives and additional devices. Please take the board out of the chassis and test it with minimum configuration (Motherboard, processor, power supply, 1 memory stick and video card)
- Remove the CMOS battery and leave the system without it for about an hour. Then put it back on and restart the system. http://www.intel.com/support/motherboards/desktop/sb/CS-028780.htm?wapkw=clear+cmos+battery#datetime
-Start adding one component at the time until you find the conflicting one.
Regarding your RAID, please let me know which Intel® Rapid Storage Technology version are you using?