The install can be very slow, because FlexCel code is big, uses a lot of generics, and Delphi compiler is really slow at compiling generics. And the new LLVM compiler is probably slower than a C++ compiler. Sadly it can take more than 1 hour to install everything, especially if you are installing the iOSDevice support for XE4. Was step 21/168 iOS?
The first thing to look would be if you have any activity in the computer while the installer hangs. If you open the task manager, is there a dcc32, dccios, or similar process running and using most of the cpu of one core (and lots of memory too)? If there is such process running, then you will need to wait for it to finish. As said, sadly the speed of the new compilers is nowhere near the famous speed of delphi since turbo pascal 1.0. It is way slower, and we have to install a lot of packages: for debug and release, for osx, windows32, windows64, ios device and ios simulator. This means each package must be compiled 2 x 5 = 10 times.
Please try to verify if the compiler is running when the setup appears like it is frozen. If it is, please give it a couple of hours. If nothing is running and using cpu, please look at <install folder>\FlexCelVCLNT\Setup and see if there is a file FlexCel_build_log.txt there. If there is, please post it here or mail it to me at adrian@tmssoftware.com