Why are Disk and Network columns disabled in Task Manager in Windows Server 2012?

This is because disk metrics are disabled by default on Windows Server 2012 because of significant performance impact, however, it is enabled in Windows 8.Use Resource Monitor to gauge Disk and Network IO usage. - Syed Yusuf from Microsoft R&D

If you need to see the metrics, you can use Resource Monitor.

Alternatively:

You can enable Disk performance monitoring on this tab by running the following command from a Command Prompt launched using the "Run as Administrator" option.

diskperf -y

Sources:

• http://social.technet.microsoft.com/Forums/en-US/winserver8gen/thread/db697958-b1a7-4037-b24a-846dff42fe1f/?prof=required
• http://blogs.technet.com/b/askperf/archive/2012/10/27/windows-8-windows-server-2012-the-new-task-manager.aspx
• http://blogs.technet.com/b/keithmayer/archive/2012/10/14/task-mastering-the-new-task-manager-31-days-of-favorite-features-in-winserv-2012-part-14-of-31.aspx#.UJS1iMXMiUk

Same problem , thanks for ronalchn's explanation... I will let it go. Before that ,I was searching for solution . In case someone need it:

One way to unlock this option is to hack the taskmgr.exe program. By using a reverse software like ida to edit taskmgr.exe , search IsServer ,change a jnz to six nop.

Source:

https://www.zhihu.com/question/57357900

A video is available here, you don't have to know what he says,just follow the steps.

Windows Server 2012/2012 R2/2016 Unlock all functions