Preview doesn't work correctely

[Rafaela5D36]

I've always edited using Premiere without no problems. The last days when I try to edit some simple pictures I can't visualize the effects on the preview box. I've already reconfigurated the computer and it didn't work. It's not even a problem with the size of the archieves, I've already tried it too! Can somebody help me?

[Michael Grenadier]

Please tell us your system specs: OS version, Premiere version, amount of RAM, Hardware specs including graphics card and your source properties and your sequence settings.  When you say "preview box" do you mean the program monitor?