You should add your camera type to your signature or profile, this way we know what camera you're using - we could also suggest software / converters then...
...but since we don't know your camera model, we don't know whether e.g. DCRAW or DNG4PS-2 can convert your images, also we can't say whether viewers like XNVIEW, FASTSTONE IMAGE VIEWER or Google's PICASA can read (and save / convert) your images...
Does that happen (makes changes to settings) when you unlock, use, then lock the SD card?
As whim said - no, definitively not; i guess you accidentialy pressed the RAW ON / OFF shortcut key on your camera...(which one ? - i don't know your camera, so i don't know your short cut - maybe DISP in <Alt> mode ? )
There's no need to re-install CHDK; just reset the CHDK configuration to the defaults: menu Miscellaneous stuff -- Reset options to default...