How do I fix my computer after messing with BIOS

Hello Jacob. When a PC has no display and no USB power, especially after some things were changed in BIOS BIOS settings related in particular to changing Secure Boot options to Custom and changing the platform keys, this signifies that the firmware can not be properly loaded, or that it has encountered a corruption which is preventing the system getting past POST (Power-On Self-Test). Fans and lights turn on, but the motherboard is stuck in a failed security state due to an invalid or missing Platform Key (PK).

The PK is important for validating Secure Boot. Since you already attempted to reset CMOS, remove battery then flash BIOS, this issue is likely the Secure Boot database being corrupted or locked.

What you can do is:

1. Disconnect all peripherals
2. Remove any GPU if accessible
3. Boot only with CPU, one RAM stick and onboard video if any.

Last is to resetting boot secure keys. If possible go to BIOS and find Secure Boot options. Then select the "Restore Factory Keys". If you could not get to BIOS then there are maybe another recovery options that are available for your motherboard. Some boards can do a USB BIOS recovery through some particular port and file naming convention. Remember to connect the monitor to the correct output, such as HDMI on the motherboard, if a GPU was removed.

Here's the reference: Easily Fixed Black Screen after BIOS Update on Windows 10/11

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Best regards,