FZ330 File Issue

I bought an FZ330 last week having previously owned an FZ150 & Fz1000. I usually shoot video in MP4, but having read Graham Houghton's set up tutorial, decided to use AVCHD as suggested. I shot some trial footage but when I tried to view the files in Windows 7 Professional, nothing was showing. I thought I wasn't pressing the correct buttons & had another couple of goes, nothing. So I re-set the camera back to record in MP4, bingo the files were there, has anyone a suggestions why?

