PROBLEM SOLVED:
I'm using Windows 7 as well, with 4GB RAM. Some sites are saying it has to do with Internet Explorer 10 in combination with a certain update, but I'm using Internet Explorer 11. Scans and fixes didn't help. I found out it had to do with some thumbnail preview malfunction in Windows explorer, especially with 3D MP4 files. Each time I opened a folder with a 3D MP4 file, the problem occurred. So I downloaded Media Preview from Babelsoft (http://www.babelsoft.net/products.htm) and only selected the MP4 files group for being previewed in Windows explorer. Problem solved. Later on I found out that it is because of Windows Media Player not being able to play those 3D MP4 files. A thumbnail can't be created so the whole 3D MP4...