Hi, I would try opening it up and check around the area where the power supply is located. This guide covers the opening process: Replacing Sega Dreamcast Power Block (Power Supply) You will most likely find a burned component in the power supply board. If you own or have access to a soldering iron, you could try replacing the damaged components. Alternatively, could buy a new US Dreamcast power supply on eBay for around 20 dollars and replace it with the faulty one.

Hi, Much like other posts, this problem occurs whenever there’s a short circuit or when cables are disconnected in the device. I would try opening it up and reseating the screens ribbon cables which can be located on the far top right of the motherboard.