Xbox 360 SLIM RGH 3 won't start

Hi. I've been having a problem with my Xbox 360 SLIM with RGH 3 for a while now. Around the beginning of the year, I tried to turn on the console, but it wouldn't start. When I pressed the power button, I only heard the startup sound, the main LED lit up, the fans ran at 100%, and that was it. I waited a few minutes, but nothing happened, so I unplugged the console. After that, the console only played the power-on beep and the disc ejection sound. There was no other response—I couldn't open the drive, not even the LED lit up. Yesterday, I tried the console again, and surprisingly, the console "started up"—that is, the LED lit up, I could open the disc drive, but that was it. I tried accessing Xell, and it worked normally and displayed the error message on the screen. I tried turning the console off and on with a wireless controller, but the console only displayed the E72 error message. So far, I haven't been able to turn Xell back on, and I don't know what determines whether the console "starts up." Could anyone help?

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