HP ProDesk 600 G2 Mini - Powers On, No Display, but POST Beeps Work. Extensive Troubleshootin

[Pierpatrat]

Hello everyone,

I'm hoping to get some expert advice on a very stubborn HP ProDesk 600 G2 Mini that I'm trying to fix.

System Specs:

• Model: HP ProDesk 600 G2 Desktop Mini
• Issue: Powers on (fan spins, power light is on) but there is absolutely no video output (monitor shows "No Signal").
• Connection: PC's DisplayPort to Monitor's HDMI port (using a DP to HDMI cable/adapter).

Problem Description: The PC was working perfectly fine. I shut it down, unplugged it, and moved it to a smart plug. After plugging it back in, it would no longer output a video signal. The power light turns on and the CPU fan spins, but that's it.

 What I've Tried So Far (Troubleshooting Steps Performed):

I have gone through an extensive troubleshooting process, and I want to list everything to show what has already been done.

1. Basic Checks:

• Verified that the monitor and the cable work perfectly with another device.
• Tried both DisplayPort outputs on the back of the PC.
• Removed the smart plug and connected the PC directly to a known-good wall outlet.
• Attempted a "minimalist boot" by disconnecting everything except power and video (no storage drive, no keyboard/mouse, etc.).

2. Internal Hardware & CMOS:

• RAM: I have reseated the RAM. The most important finding is that if I remove the RAM modules completely, the motherboard correctly produces the audible error beeps for missing RAM. This tells me the CPU, motherboard speaker, and at least a fundamental part of the POST process are working.
• CMOS Reset: I have performed a full CMOS reset using two methods:
  • Removing the CMOS battery for over 15 minutes.
  • Using the yellow onboard CMOS reset button.
• PSU: I have tested the external power brick with a multimeter and it correctly outputs a stable 19V.

3. Advanced BIOS Recovery Attempts: This is where it gets detailed. My main suspicion was a corrupted BIOS.

• Initial Failure: My first attempt at creating a BIOS recovery USB drive failed. I was using an SD card inside a USB adapter. When I put this into the broken PC, the device's LED would not light up at all, even though a keyboard's LEDs would.
• Successful USB Creation: I have since acquired a proper, native 4GB USB 2.0 flash drive. I used the HP BIOS utility (sp151021.exe for BIOS N22 v02.60) on another computer and successfully created the recovery media. The utility confirmed a successful creation.
• Forcing Recovery Mode: Since key combinations (Win+B, Win+V) did nothing, I opened the PC and moved the blue jumper labeled BB (Boot Block) to the recovery position (from pins 1-2 to 2-3).
• Current Status: With the BB jumper set and the new native USB stick inserted, there is progress!
  • The USB stick's activity LED now lights up with a solid light (it does not blink).
  • A wired keyboard, if connected, also lights up. This confirms the USB ports are receiving 5V power.

My Core Question / Where I'm Stuck:

Even though the PC is in Boot Block recovery mode and the USB stick is clearly receiving power, the recovery process never seems to fully initiate. I have left the machine in this state for over 15 minutes.

• I do not hear any beeps to indicate that the recovery is starting.
• The USB stick's light remains solid and does not start blinking (which I would expect during a file read/write operation).

Given that the motherboard is "alive" enough to beep for RAM errors and to power the USB ports, but won't start the BIOS recovery from the Boot Block, what could be the next logical step? Is it possible for the BIOS boot block itself to be corrupted in a way that it can't read the USB, or does this point to a more subtle motherboard failure (e.g., a chipset or I/O controller issue)?