> Now, I've opened the case (puh!) and tried fiddeling with the modules,
> trying to start it with fewer modules and so. Still no life. So, I'm
> wondering, can one place the memory in the 3100 the wrong way?

At least in a ds3100 they are placed like this (ex. with 6 modules):
|= module
-= empty socket

|||---|||--- (back of ds)

> I've also got a DS 5000/120 which works great. Now, the cable between
> the 3100 and the monitor fits right into the DS 5000's keyboard/mouse
> port and has sockets for keyboard and mouse on the cable. Can I use
> this cable for connecting the keyboard/mouse to the DS 5000?

If you explained right, you have an authentic DS keyb. cable. 

> Further, does anyone in Sweden have an unused cable between a PMAG-B
> and a VR290-D3 monitor (3xBNC)? I'd be interested in buying that one
> if so :-)

If you get hold of a 3W3 connector you can easily build a cable 
yourself!

Joachim Buss