Mysterious reboots can be a symptom of overheating another common cause is undersized or poor quality psu. What is the mobo? Are the cpu and mobo temps monitored by the bios? They can be set in the bios if they are and the mobo manufacturer may have a monitoring software so you can get a heads up before an ill-time reboot.

If you have any trouble getting the second drive spun up, just holler and provide the particulars.