so, the laptop is connected to the DM via toslink?
The obvious checks (at the risk of being really obvious sorry):
Which laptop is it, as optical s/pdifs are rare on portable machines.
Check you have got the DM switched to the correct optical input (there are two).
Check your amp is set to the right input selector - is it working from other sources ok?
Failing that,
What are the output settings for the laptop, and what media player are you using? You'll need to make sure that you have configured windows to play optical out as default, unless your media player over-rules this (as J River for example can do if that's how it is set).
To check this, go into control panel, or simply right click on the audio icon in the taskbar and click on output device settings. You should open up a screen that shows you the connected audio devices - so built in speakers, optical s/pdif, or whatever other software drivers were installed (for example the DM uses its own ASIO driver that would also show as an option if installed and connected.