Are you sure it’s the RPi and not the SD card? I’ve had a couple of SD cards get corrupted, and this results in the power/RED light coming on, but the ACT/green light only comes on briefly. Changing out the SD card to a new one with a fresh copy of the OS fixed this in both cases. I had been using a couple of cheapo 8 GB SD cards, both of which failed. Some new SanDisk class 10 16 GB SD cards fixed that problem, though I really don’t need that much memory for the OSPi’s purposes.