I have experienced a very confusing problem with qt and I share my experience with you.
if system date at the qt installation time is ahead of the date after qt installation, for any reason (for example I corrected my system's wrong date after qt installation), you can't compile your qt programs and a command is infinitely executed when you issue the make command.
the reason is, project configurations for making qt programs depend on some files in the qt installation, and every time .pro file is re-generated it has still an older date that the qt's files.