PC won't boot after BIOS update, PSU fan becomes extremely loud

[Luke2512]

Hello! I recently purchased a second hand ProDesk 400 G1 SFF PC. The PC would boot fine with everything in working order. After expriencing trouble with a fresh Debian install, I was advised by a colleague to carry out a BIOS update to ensure compatibility with the version I installed (12.5.0). I installed BIOS version L02_0256 witht the BIN file via USB. There were no power cuts and i recieved a small green box afterwards saying it had completed successfully. I pressed OK and the computer turned off.

After about 5 minutes of inactivity I noticed the fans getting concerningly loud. After about 20 seconds it sounded more reminiscent of a fighter jet than a desktop pc. I quickly realised it was the fan inside the PSU. It continued like this for about 5 minutes before I decided it was probably stupid to leave a power supply running like that for long, so I decided to shut it off via the power button. Now every time I power the PC on, it will do the same thing, waiting about 20 seconds before starting to spin at extreme speeds.

I have tried using a USB flash drive formatted with FAT32 and the binary files provided with the site but the PC does not seem to pick up any sort of input.

More information which might be useful:
- I upgraded from BIOS version L02_0211

- The motherboard seems to recieve power as a small light marked "AUX" is on while the cable is in.

- The CPU fan and hard drive both recieve power.

- There is no video output through DVI whatsoever. Unfortunately I cannot test with VGA.

- Both memory sticks (2 x 4GB) and the CMOS battery are brand new (both replaced and working prior to BIOS update).