This may be relevant to some of you, and may not. But I just had the same issue with a 380 Hw3, so well out of warranty. In my case, I got the standard beep noise on power up, as you would from an old computer. So, I figured that it is actually working, but it does not start the boot sequence. As there are no easy way to connect a monitor to see what is actually going on, I remember from the old days, that on a bios-halt, you had to press a key on the keyboard for it to continue booting. So I connected a keyboard to the usb connector in the front, waited until after the start-up beep (and then some), then I pressed F1-key. And, magically it started booting. I suspect this started happening due to a completely drained battery.
Please let me know if this worked for some of you. Best of luck.