The emulator boots to a solid red screen. This means the BIOS decryption key failed. You likely have a header-less dump or a file that was padded with zeros. Solution: Dump your own BIOS using BIOS Dumper homebrew on a real PS2.

: When the emulator starts, it "boots" this BIOS file. The BIOS checks the virtual memory, processors, and DVD drive. The "Startup" Experience

The SCPH70012BIOSV12USA200BIN file is a specific version of the PS2 BIOS, designed for use in the United States. Let's break down the filename: