Open MATLAB.. File - > import ->.dat file foolow steps to import the .dat
file into the MATLAB workspace.
From the MATLAB command line, open the signal processing tool by typing:
sptool
From sptool, click import and select the matrix you stored your dat file
in.. click the arrow to set the sample rate (depending on how big your data
set is, type 1000 for example
This should import your data set and you could view it by selecting it.
On the right, you have a list of Spectral options, including PSD.
That's the gist of a method I would try.
Ger