Be sure to check the seating of the CPU and Memory, either of those can cause the bios to go wonky.
If there's a "clear cmos" jumper / button on the board, I'd try that.
After that, I'd get a power supply tester and a motherboard tester and use them. They can be helpful to have as a PC builder in any case.
Good luck and I hope you share what the eventual solution was.