Check your associations - when you run a perl script from Windows, it is usually associated with pl2bat (I have not used Windows in a while - the bat file name may have changed) - which is supposed to pass in arguments thus:

perl -w scriptname.pl "%1" "%2" "%3" "%4" "%5" "%6" "%7" "%8" "%9"
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It is likely that in your windows 8 case, the arguments %* are missing in the bat file that invokes the script.

To avoid this, Try running your script like this:

perl testarg a b c
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and post your results.