[SOLVED]I have an annoying problem – Please Help.

Basically, all of a sudden, all pictures and video files had there file type at the end of their name. So for example an episode of Prison Break that I downloaded would be called:
Prison Break – Season 1 – Episode 1. What I am trying to explain is that something has changed.
So now it reads: Prison Break – Season 1 – Episode 1.avi
and I can’t change the .avi part, if I do I can’t play the file. Okay it’s not a major problem but it is annoying me.
If you don’t understand, there are screen shots below. —————————————————————————————————————————————————————–
As you can see here, there’s a few videos in a folder. http://f.imagehost.org/view/0583/Annoying_Problem_1
Now on the second screen shot I’ve removed the .avi from the bottom video and this message appears! Why!? That was the original name of the file! I don’t want the stupid .avi at the end of my videos! http://f.imagehost.org/view/0027/Annoying_Problem_2
Now on the third screen shot you can see that I’ve removed the .avi and now the file is of no use. I can’t open it because I’ve changed the file extension. http://f.imagehost.org/view/0283/Annoying_Problem_3
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Heres another example.
Below is just a new text document which I created in a new folder. Again it has it’s file extension at the end, why I do not know. http://f.imagehost.org/view/0360/Annoying_Problem_4
Once again, I’ve removed the extension and now the file is unusable. http://f.imagehost.org/view/0086/Annoying_Problem_5
This is happening with all files, and it’s bugging me as it wasn’t doing it before. Can anyone explain why? Any help would be greatly appreciated.
Answer #1
Re-add .avi to the files you had removed it from.
Open up “My Documents”, go up to Tools > Folder Options, click on the View tab. Once in there, scroll down until you see “Hide extensions for known file types” and check that box, that will remove the .avi at the end of your files.
Just be sure to add .avi back to whatever you need FIRST before you check the hide extensions.
Answer #2
My computer > Tools > Folder options > View..Untick “Hide extensions for known file types”…Apply..
Answer #3
Problem solved, thanks very much guys. Not sure how it I managed to change it! Thanks again.
Answer #4
Solved Tag added. -