Lenovo thinkcentre error boot sequence

so it wont boot screen would turn on say "no signal" than monitor would turn off.
i tried taking out the ram and putting it back in, I tried taking battery out, I tried the f8 on start up and got a menu to come up so I changed it back to default and the computer turned off and upon rebooting it gave me 1 beep and a error message says "error boot sequence" than takes me to a blue screen wich gives me options to turn off computer??? please help me