Could be NIC lock ups.... driver issue usually in this case I guess.

i agree, hard reboots by itself would indicate a hardware issue.
run a RAID health check from the system BIOS, and see how that comes out. If you can get logs from the controller, that may give you some information as well.

You can also boot the trial version of DSSV6 in 32bit mode, and see if you can present the volumes with no error. If so, upgrade. R3 is EOL anyway, and if the DOM is unrecoverable, an upgrade should be considered.