The OS Drive is a Western Digital SATA 400Gb WD4000AAKS Caviar SE16 (bought June 2007), split into two partitions, one for the OS and one for programs. The other two drives are also Western Digital, used for data and photos/video etc.
I'll dig out a new SATA cable later today and keep it ready to try it on another header. I want to run the computer "as is" with the weather software shut down for a few days to see if the freezing still happens. If it does then I'll start reseating things and then change bits one by one. Thanks for all the suggestions so far.
