This is actually deceptively simple. It relates to the ORDER you do things in, The simple answer is you have shared the wrong network. A lot of "howtos" tell you to do it in a orde that CANNOT work.
The correct order is covered here
(Step 1) In Windows 7 go to Change Adapter Settings (Open Control Panel and go to Network and Sharing Center. Click Change Adapter Settings.) have a look before you start any of this there will be at least TWO icons. a LAN icon and a WIFI icon. At least these two.
Now run this (Step 2):
@cmd as admin:@ netsh wlan set hostednetwork mode=allow ssid=mywifi key=passphrase
@cmd as admin:@ netsh wlan start hostednetwork
You will immediately see a NEW icon appear in Change Adapter Settings this is the actual connection that needs permission to share.
(Step 3) Back to the Change Adapter Settings window. Right click your Actual Internet LAN connection icon (on my PC is is called "Local Area Connection" the icon has a little RJ45 connector symbol on it and the grey text says "Realtek PCIe GBE Family Controller" it has no red ticks on it and it's the internet connection for my windows 7 pc, which I know because if I disconnect the LAN cable from the back of the pc, it THIS icon that goes ill on me) and select Properties. Click the Sharing tab. Choose your new virtual Wi-Fi adapter that appeared after step 2 and click OK.
NB: the new one that appeared will have the grey text "Microsoft Virtual WiFi Miniport Adapter" under a name like "Wireless Network Connection 2"
Then right click the new virtual Wi-Fi adapter that appeared after step 2 and disable all the gubins except TCP/IP v4 (un tick them all under Networking tab except the "Internet Protocol Version 4 (TCP/IPv4)"
it was this website that helped me figure it out http://mintywhite.com/windows-7/set-windows-7-wifi-hotspot-quick-tip/