The diagnostic light table never mentions anything about blinking lights on the back panel but the USER GUIDE
does mention the power button blinking amber...
If the power light is blinking amber —
The computer is receiving electrical power, but an internal power problem might exist.
* Ensure that the voltage selection switch is set to match the AC power at your location (if applicable).
* Ensure that the processor power cable is securely connected to the system board.
Sounds like the PSU or motherboard. Got a spare power supply or someone you could borrow one from?