Video Can't be Displayed in Photo Gallery

Hi, I'm Todd Pretty New to TechSpot. I have a problems with Windows photo gallery. Someone in family or even me did something I can't figure out. I have pictures and video in photo gallery. OK, I went to view videos, went to click on one then it shows "Video Can't Be Displayed". It shows under video clip at like 007.MOV I know it wasn't like this before it was something else like .mpg I believe. I'm not sure what happen. I'm trying to change all the format in gallery back to the original file. I do know i was trying to make a movie and I close the movie maker for night then next day all videos in gallery was showing video can't be displayed. Now all the videos I had in maker are gone, what happen I kinda like to know. Need help, Anyone? I really appreciated any help. I'm using Windows Vista Photo Gallery. Thanks and Have a great day. Todd

I have my video fix in windows photo gallery. I downloaded codecs from k lite. It works pretty good. I guess all the extension files got whacked out of place. Why or how I don't know. HP customer support told me it was my codecs on computer. I deleted Dixv and download codecs from k- lite codec pack. So far so good. Have a great day everyone. Todd