@Saelic Vogel: yes, I did this on-by-one, not all at the same time.
OK, I removed the power cable, switched the "BIOS defaults" jumper to on, and removed the battery for ~1 hour. Then I reversed it all and powered up the machine. No changes. Fans are spinning, front panel LEDs are on, video output is dead. I have no rear POST error LEDs and those on the motherboard are turned off.
I don't quite remember what was the BIOS version prior the upgrade. I think it was 00.5x. I tried to upgrade it to 00.63 (ZIP file name: UR_12_12_2012_BIOS63_BMC61_FRUSDR26_ME112.zip).
Thank you for your help.