HP Workstation xw4400 Beep Codes

Question

My infant son repeatedly pressed the power button, now when I press the button all I get is 4-4-4-4-4 beeps. I removed and unplugged everything one at a time and still get the beeps. The only thing I didn't unpulug is the fan that isn't spinning do you think this could be the problem. If not then what.
Thank you