How dd this happen!?

I have a problem, ive got a red dot of death and i dont even know if thats possible the Xbox is 8 years old now but now it wont even start up, it used to sometimes give the RDOD but now it starts green whirs the drives and then RDOD appears, and i need to know what causes this beyond, oh the power connecters lose or some crap like that, can someone tell me whats wrong here?