This happened to me with C7Pro. Here's a little test for you to try: Find the Carrara executable, then RIGHT click on it and "Run as.. Administrator". If you can now use Carrara as usual, then it has to do with permissions and security software and secret license files.
In my case, DAZ thinks that it is zone alarm messing up my install. I have had to set up a workaround for myself.
If executing the program as "administrator" (NOT your usual ID, even if you have administrator rights!) makes it work, then I can point you to what worked for me.