My Power Mac G5 cannot even enter Open Firmware console

Hi,

My Power Mac G5 (late 2005, DP) became to be unable
even to enter Open Firmware console.

This symptom starts after loading aarch64 ELF kernel
image from tftp by mistake :(

After this accident:

(1) Enable to power on.
(2) Boot sound rings just once.
(3) No signal to DVI ports.
(4) After few ten seconds, CPU fan becomes noisy.
(5) Then, no response any further.
(6) During (1)-(5), red LED on logic board lights (no blinking).

I tried:

(a) Keep unplugged AC cable over a night.
(b) Push SMU reset button with and without power on.
(c) "Command + Option + P + R" from USB keyboard
---> only single bell
(d) "Command + Option + O + F" from USB keyboard
---> cannot enter Open Firmware console

But nothing works.

Does anyone have idea to fix this?

Thanks,
rin