|"I attached everything to the new motherboard"|
There was your second mistake. ( The first was thinking a bios flash would solve the original problem)
Take everything back out. Benchtest the new motherboard.
This is done by connecting only powersupply, CPU with fan, keyboard, 1 stick of ram, and graphics. ( Use onboard if present)
Next use a screwdriver to bridge the power-on header pins and see if you can get it to load up into BIOS.
Post back with the outcome of this test and we can then proceed to try to identify which of the other devices is causing the problem. I suspect a faulty drive or cable or maybe bad ram
Goin' Fishin' (Some day)