My helloworld program can run in Qt Creator but can't run when I excecute the .exe file

I built a GUI helloworld program, using Qt Creator 2.6.1 with Qt 5.0.0 on Windows 7. The program runs successfully when I click the “Run “ button in Qt Creator. When I found the exe file in a directory like “helloqt-build-Desktop_Qt_5_0_0_MSVC2010_32bit_SDK-Release\release” and doubleclick it, it reports error like “missing Qt5Widgets.dll”. So I copied needed .dll files from the directory of Qt libs to the same directory with the .exe file, and then when I doubleclick it, nothing happens. Why doesn’t the program run when I doubleclick it? Could you tell me where am I wrong? Thanks a lot for your help.