I suggest starting out by getting a decent media player onto your computer. Download and install either VLC or GOM. (VLC is the media player most widely praised by the technical press; although it's very good, I prefer GOM myself):
http://www.videolan.org/vlc/index.html
or
http://player.gomlab.com/eng/download/
(As usual, you need to download the file and then double-click on it to run the installation program. When asked which file types you want to associate with the program, simply accept the defaults).
Once that's installed, try putting the SDHC card into your computer's card reader again. If nothing happens that doesn't necessarily mean that it's not recognised; go to 'My Computer' and double-click on the icon for the card reader to see if the contents are displayed. (If you just see a folder there, double-click on it to open it; you might also need to do that for a further folder, depending upon how your camcorder stores files). If you don't know which icon is the right one for your card reader, just keep trying them until you get success. (If you click on an icon for the wrong slot you'll simply see a message telling you to insert a card; you can't damage anything!).
If you can access the files that way, double-clicking on one of them should open it in VLC/GOM.
If you can't access the files via your computer's card reader it might be because of a fault with it (or possibly because it doesn't recognise HD cards). Try again with an external card reader plugged into a spare USB port. It won't cost you much!
http://www.poundland.co.uk/product-range/a-z/signalex-multishot-usb-card-reader/
It might also be worth trying the SDHC card with a friend's computer; if the videos still appear purple it suggests that there's either a fault with the camcorder itself or with the settings you've applied to it.
Chris