Get the Windows 7 X64 LAN driver, probably the Realtek one. There is also an Atheros driver but go with the Realtek driver. Download and install that one. See if that helps.

See here: Satellite L755-S5253

Atheros LAN Driver
Posted Date: 2016-09-19 | Version: 1.0.0.46 | Size: 6.79M

Realtek Wireless LAN Driver
Posted Date: 2016-09-19 | Version: 2.00.0013 | Size: 17.78M

Realtek Wireless LAN Driver
Posted Date: 2016-09-19 | Version: 2.00.0013 | Size: 17.8M

If that installs then right click on the LAN in Device Manager and select Update driver.