New RPi4 not booting or showing image with FAN SHIM installed

I have just bought the new Pi 4 4GB and I’m powering it with my old 2,5A official pi3 power supply and a usb-c adapter. The red LED turns on and the green LED blinks, however neither my set-up Buster system or a fresh install on a SD card are showing anything on a HDMI monitor (through the official HDMI adapter) on ports 0 and 1 or are connecting to the wired network.
I am flashing the official Raspbian Buster image using Balena Etcher.

Could it be a problem with the Pi?

Edit: I removed the FAN Shim I bought with it and everything worked as expected… Why would the Shim interfere with the bootup?

I have flagged this to pimoroni support as your question this far is unaddressed. whilst you are using an , " underpowered" (recommended 3A) PSU with an adaptor , it is surprising that the pi boots without the shim but not with it. and the shim (as far as I am aware ) uses very little power/ current.

Take a look at this thread. Underpowering causing issues when combined with a fan

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Hi,

As NotAfan has posted it might be power issues, especially if you’re seeing the lightning bolt symbol at all when the Pi is powered up without the fan shim. Any chance you could test an alternative power source, ideally one that offers at least 3A?

Cheers,

Matt

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After I booted I installed the fan, stressed the cpu and everything stayed stable, also I haven’t seen the lightning bolt symbol.

And for some reason after the first boot it started booting with the fan shim. However I will buy an apropriate power supply soon, thanks for the help.