If it won't POST, how did you verify which video adapter was active?
As to the power problem, the first issue is that the board is set to recover "ON" from power loss. This is pretty normal for servers, and can be corrected in the BIOS setup.
A rebooting loop can be many things. A condition is being set upon self-check that the machine "thinks" requires a reboot to correct. Many times this has to do with boot device order, or the devices themselves. Disconnect all drives, optical, magnetic, and flash.