SQLServerAgent could not be started (reason: Unable to connect to server '(local)'; SQLServerAgent cannot start).

If SQL Server agent not started and if you find below error in event viewer

Error Details

 Log Name             :         Application

Source                  :         SQLSERVERAGENT

Date                      :         8/8/2017 3:49:43 PM

Event ID               :         103

Task Category      :         Service Control

Level                    :         Error

Keywords             :      Classic

User                      :          N/A

Computer             :      VmSQLServer

Description           :

SQLServerAgent could not be started (reason: Unable to connect to server '(local)'; SQLServerAgent cannot start).

Solution 

Provide instance in  in "ServerHost" under

HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Microsoft SQL Server\MSSQL12.MSSQLSERVER\SQLServerAgent

Goto run
type regedit
expand HKEY_LOCAL_MACHINE --> SOFTWARE --> Microsoft --> Microsoft SQL Server
click on SQLServerAgent in Microsoft SQL Server
In right side pane double click on ServerHost and provide instance name under  value data

NetFx3 error while installing SQL Server 2012 on windows 2012 server

Problem description

TITLE: Microsoft SQL Server 2012 Service Pack 1 Setup

The following error has occurred:

Error while enabling Windows feature : NetFx3, Error Code : -2146498298 , Please try enabling Windows feature : NetFx3 from Windows management tools and then run setup again. For more information on how to enable Windows features , see http://go.microsoft.com/fwlink/?linkid=227143

For help, click: http://go.microsoft.com/fwlink?LinkID=20476&ProdName=Microsoft%20SQL%20Server&EvtSrc=setup.rll&EvtID=50000&ProdVer=11.0.3000.0&EvtType=0x681D636F%25401428%25401

- 

Solution 

Goto server manager

 --> Click on manager right side corner of window

--> Click Add Roles and Features

Blow Add Roles and features wizard window appears 

click on next

in the next screen click on Role-based or feature-based installation

and click on the next

in the Server Selection Screen select the first radio button i.e. Select a Server from the Server Pool 

In the server pool window you can see the server name 

On Server Roles page simply click on next

in Features page wizard clicked on the check box next to ".NET Framework 3.5 Features", and then clicked on the Next as shown in below image

and in final wizard click on install to add features

and installation progress as below 

Thanks & Regards
Venkat Sangu