Ahh, my mate had the same problem..
I think it's a problem of certain circuits inside dc getting "oxidized"
thus generating errors and boot up's (sorry for my bad english
)
check this site out:
http://dc.konsolifin.net/spesiaalit/...hp?juttuid=510
Even though it's in finnish you should get the big picture
First you have to open your Dc and take the modem out..
I guess your dreamcasts' problem is a "connection error" between the components shown in the picture.
What you have to do now is to "scrath" the surface of that component clean.. be careful..
Remember that im NOT gonna take any responsibility for any damage that you've caused.