Please ensure that your windows machine meets the minimum specifications 3CX phone system requires to run.
Check this link http://www.3cx.com/docs/installing-3cx/
If there was a previous installation of 3CX on the machine make sure you uninstall everything. Check C:\Program Files for any 3CX folders and delete them. Do the same for C:\ProgramData.
Also make sure that your windows machine is full up to date, if not perform all windows updates and restart your machine.
Disable any antivirus software on the machine (just to make sure) and re-download the 3CX installer.