i have changed the BIOS for many 2011 logic boards but all of them become slow after that. why? Any one can help me?

To check where the problem is if the power light is on,then you need to check the fan to see if it dont run, it may be the A1370 keyboard or A1369 keyboard , or the logicboard problem if the power light is not on, it may be the magesafe power DC-IN jack problem If you want to solve this problem completely,you may as to find a technician