I have perl scripts which were running in Windows 7 just fine as of this morning. I made the mistake of using NotePad as the default for opening/editng my .pl files. Now, when I attempt to run the unedited .pl files from a DOS prompt, the script does not execute but opens the associated source code file in Windows Explorer. This is the same for all my .pl files no matter the complexity (including classic "hello world".
I have been researching changes need to the registry - it all looks fine. Tried assoc and ftype changes - nothing. Tried reinstalling ActivePerl - no solution.
Sounds like your .pl extention association is now set to Notepad rather than perl.exe. If you are too busy to fix that, just type "perl yourscript.pl" in a command promot window to start the perl interpreter and to send your script to it to run.
See this answer to fix the association:
File Type .pl Association and Using cmd.exe to Run the Script