The computer cannot starting, but period of time have been able starting

The computer cannot starting, but period of time have been able starting, has this kind of situation frequently, I have also made power source’s plug, but also does not have what function, what is strange computer period of time have been also good, what reason is, how should solve?
1.the power source got older, trades one newly, pays attention to the power source to have the high pressure, oneself do not do.
2.CPU overheated, trades the high powered the CPU ventilator.Strengthens the radiation is the key!