quicktime icon changed to a lock icon??!

i have an imac g5, OS X 10.3.9. i was getting ready to burn a cd of my photos and video clips. my video clips typically show up in my folder with the blue Quicktime icon next to them. but suddenly those blue Quicktime icons show as another type of icon when items in that folder are viewed as a list, or as a tiny lock when viewed in their folder as icons. what does this sudden lock icon mean? i still seem to be able to play the video clips fine on my computer. the concern is that if i burn them to a disc to be played in other computers (mac AND PC), will they be viewable? and what does the lock mean? how can it be undone? someone please help me get rid of the lock!