The Dead PC.
There are so many good prior dead PC discussions and how to troubleshoot that I can't match that here.
The symptom is typical for failed motherboard and or PSU.
Have a HP p2-1394 Desktop PC all of a sudden when I turn it on, the lights and fans come on, but no video? Tried 3 different monitors and cables nothing. Took out the memory out, there are two, installed one the computer turned on the turned off kept doing this. Tried the other same thing. Tried another different memory stick same thing? Put back the two sticks now it turns on and off constantly? What could be the problem??

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