Hello,
Thank you for posting your query on Microsoft Community Forums.
As per description, you are unable to share LAN Internet Connection using Wi Fi.
I would suggest you to follow the steps given below and check.
Method 1: Follow the steps:
1.Go to your network icon after connected your LAN cable. Click on " Open network and sharing center."
2.Then click "Local area connection" > "Properties" > "Sharing" Tab and check "allow other network user..." Then click OK > close.
3.back to network and sharing center. Go to "Set up a new connection or network"
4.Choose "Set up a wireless ad hoc" > Next
5.Type in Your connection name like you want, in security type I recommended WEP.
And in security key, input numbers and Characters like C6774663DD for password.(It won't allow too easy password.)
If you want to use this network many times, check "Save this network."
6.And then just ask your friends to connect to your wifi network with password you set in the first time.
If issue still persist try method 2.
Method 2: I would suggest you to follow the steps from the article given below and check.
**Note:**The article is for Windows 7. It also holds good for Windows 8.1
Refer: Set up a shared Internet connection using ICS (Internet Connection Sharing)
Hope this information is helpful. Please do let us know if you need further assistance with Windows.