I've found the solution!
And it works 100% sure!
First, open regedit (Start > Execute > Regedit or c:\windows\regedit.exe)
make a backup (file > exporting)
In regedit, search for "videoborder"
You'll find some keys like that :
NVZORAN.525@60Hz.videoborder
NV36ZORAN.525@60Hz.videoborder
NV36ZORAN.625@60Hz.videoborder
NVZORAN.625@50Hz.videoborder
....
(the name depends on your nvidia graphic card but it's always followed by ".videoborder")
The set number should be 01 00 00 00
But some of them have this number : 00 00 00 00
If so, modify the number and correct it so that a "1" appears on the second number : 01 00 00 00 like it should be.
once again the correct answer is for example...
NV36ZORAN.525@60Hz.videoborder = 01 00 00 00
Close regedit when every key has a one in it.
Reboot you're computer for the changing to take effect.
Then you can open your videos in full screen, it'll never zoom in like it used to!
It's fixed, finally!!!!
Good luck and happy viewing!