How come I can't play a video with AVCHD format on my laptop? My laptop is an HP Pavillion DV7

Try to use Leawo Video Converter to convert your video to MP4 video and then use your computer to playback it.

You could convert the AVCHD video files to standard video format like .WMV(windows media player), .MP4/.AVI(VLC media player), .MOV(Quicktime), .RM(Realone player) ect.

Each of the AVCHD camcorders ships with software designed to playback the files on your computer. Sony's HDR-SR1 and the newer HDR-SR5 both record video in the AVCHD format and ship with the Picture Motion Browser, which plays back AVCHD files on most computers. If you purchased one of the Panasonic AVCHD camcorders, the included HD Writer should allow you to playback video recorded with your camcorder.
  

While the bundled applications work, my personal preference, is Cyberlink PowerDVD Ultra, which supports playback of the AVCHD files and a whole host of other high definition formats. In addition to playing back your HD camcorder files, PowerDVD Ultra plays back Blu-ray and HD-DVD disks (with the accompanying drives connected, of course). PowerDVD Ultra also makes it possible to expand your HD video editing options, by using the included codecs to render the AVCHD video in apps like VirtualDub.

Cyberlink PowerDVD ultra can be downloaded from here : 

http://www.cyberlink.com/downloads/trials/powerdvd/download_en_US.html