PC wont boot after swaping 5600 cpu for a phenom 2 550

[Guest]

Hello, I have a a770de+ asrock mainboard a 5770 graphics card and 2 250 gb hdds and 425w psu, was running fine with a 5600 cpu but just swapped it for a phenom 2 550 and it fires up but nothing comes up on screen and it sounds as if cpu fan is whirring up and down in a pattern. Is this due to psu or faulty cpu ?

 

[simon12]

Did you update the bios before installing the CPU?