How to revert from bios 1 5 to 1 4

[sunday collins]

my ecer e machinee520 was running on bios v1.4 then after reverting to v1.5 it cannot boot, when i try to re install it cant get through, what might be the problem and what can i do to correct this

 

[frozenlead]

Are you sure you installed the correct BIOS and did so correctly?

What do you mean "can't get through"?