1. Please right click your Desktop, choose Screen Resolution and change it to recommended after your connected your computer to your TV. Does the size back to normal now?
2. Open Control Panel -> Appearance and Personalization -> Display, make sure “Smaller – 100%” is selected.
3. Open Control Panel -> Easy of Access -> Easy of Access Center, in the left panel choose Change administrative settings, make sure you did not select Apply all settings to the logon desktop.
In addition, is your TV the only display which connects to your computer? If not, please let us know how you configured your displays.
Hope this helps.