What is the most significant issue that needs to be addressed when ensuring the proper functioning of a computer?

The most significant issue addressed while ensuring the proper functionality of computer is the working of Operating System.

Explanation:

There are many issues faced while making the computer properly functional. Such as, Memory size, processor speed, software installation etc. while operating system not working properly can cause a significant problem. If operating system is not working properly, the user is unable to use the computer.

So, to make sure the functioning of computer, the significant issue that should be needed to address is Operating System Installation.