I currently use a 750 watt Power PC and Cooling PSU and 1 TB HD on my SAM with zero issues, and have used many different HW configs with the SAM with 0 issues. Everything from a 100w PSU to a 1000w Ultra PSU, 80 GB to a 2 TB HD.
Only issues I ever had with it were the SATA port issue that Slayer suggested above. Make sure you have all the drives on the right ports as per the SAM manual and it is set to boot off the CD.