I got this problem on SW 2013 with service pack 0 and also 1:

Everytime I open a file from the solidworks or windows explorer by double-clicking or drag and drop, the solid works window turns from full screen to minimized window and moves partly out of my main monitor. When the SW window is already resized, it keeps its size when a new file is opened.

It is really annoying, hope somebody already found a solution for this problem!