This can be caused by "Adobe Licensing Tool". It runs in the background and when you try to install other programs, like plug-ins, a conflict happens which causes a locked or rapidly blinking cursor. You can solve this, by running the "Adobe License Repair Tool".
The most logical answer is that your computer is either running a program without your knowledge or you have a virus. Run a full virus scan and see if that solves the issue. You could also see what process are running in your computer and if any that shouldn't be there are, end the process