hp prodesk 600 g3

I recently bought a secondhand "barebones" HP Prodesk 600 G3 Mini to build a simple linux desktop with, and it refuses to boot to BIOS. The fans are running, the CPU is hot, but it has no display output in either Displayport. PC details: Intel i5-7500 16 GB (2x8GB) DDR4 RAM 128 GB M.2 SSD PC...