When I open up the pictures that I´ve stored in "Pictures", I can´t see any
thumbnails for my picures that have the jpg ending. However, if I change it
to jpe, they show up as thumbnails! The jpeg extension however doen´t work.
The bmp pictures does however generate thumbnails.

This is a very frustrating problem. The thumbnails show up in Windows Photo
Gallery, but not in the regular explorer window. I´ve already made sure to
uncheck the "always show icons, never thumbnails"

I have two other imageing softwares installed. Is it these shoftwares that
have altered my default thumbnail generation settings? How can I turn them
back, so thet explorer also generates thumbnails for jpg and jpeg?

Please, if anyone has any idea, please help me!