PowerShell error : Install-module is not recognized as the name of a cmdlet on Powershell 5.1 with Nuget installed

HI, 

I am trying to install a powershellmodule and getting the below error message.

install-module : The term 'install-module' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the name,

or if a path was included, verify that the path is correct and try again.

At line:1 char:1

+ install-module SharePointOnlinePowerShell

+ ~~~~~~~~~~~~~~

+ CategoryInfo          : ObjectNotFound: (install-module:String) [], CommandNotFoundException

+ FullyQualifiedErrorId : CommandNotFoundException

i tried get-packageproviders and it seems to have Nuget package installed. 

Name                     Version          DynamicOptions

----                     -------          --------------

msi                      3.0.0.0          AdditionalArguments

msu                      3.0.0.0

NuGet                    3.0.0.1          Destination, ExcludeVersion, Scope, SkipDependencies, Headers, FilterOnTag, Contains, AllowPrereleaseVersions, ConfigF...

Programs                 3.0.0.0          IncludeWindowsInstaller, IncludeSystemComponent

I tried all troubleshooting steps stated in this(https://stackoverflow.com/questions/41585758/install-module-the-term-install-module-is-not-recognized-as-the-name-of-a-cm) article, but they didn't help. any suggestions?