Cannot open/view G3 videos on my please


Mu-43 Regular
I am struggling to open & view videos that I have recorded on my Lumix G3 on my PC. Searching other threads has confirmed that it is probably because they were recorded in HD quality (by default) so I have now changed this setting. This should help me for future recordings, but can anyone tell me, in very basic terms, what I need installed on my PC to allow me to view/share the videos I have already recorded. The extension of the files appears to be .DAT

I have installed the video software that came with my camera but even this does not recognise the file to open it Clearly I am doing something wrong but I cannot work out what :confused:

Many thanks