Oh flip ... my DC has decided to just keep resetting itself (cue the blue wiggle going over and over). Guess I'll be stripping it down again, hope I don't need another one - had this one since '99!
It's a common problem with the first batch of Dreamcasts which hit the market. Luckily it is easily solved (w/o buying a new one). Just open up your DC and disconnect the PSU board. It is attached to the motherboard with a 5-pin connector. The mobo draws a lot of power from the last pin which usually becomes oxidated and consequently starts to heat up quite a bit and doesn't bring enough power anymore. Just use a common contact cleaner on it and your Dreamcast will work again. Mine works fine ATM, I clean it up every 6 months usually.