Its a desktop? Great. If your computer was on and connected to internet during this lightning strike, then the LAN must have gone bust too. That is because the modem is connected to the computer, and of course passes currents, so when the lightning strike, the current must have fried your LAN Ethernet. What is confusing though is the fact that your computer still works, as the motherboard must have gotten fried a bit. I am merely assuming btw. It can't be a software issue if your LAN ethernet was working fine before the lightning strike, UNLESS, you changed your LAN Ethernet after the lightning strike.
Can you open up your desktop build, and take a look around for your Broadcom LAN Ethernet device. I am not sure if your LAN Network Device is built into your motherboard, or separate, although it is usually built into the motherboard. Check if the Broadcom LAN device is damaged or burnt or anything like that.