My router works fine for wifi but the lan connection doesn't work. Any ideas why?

Funny, I've got the exact opposite problem. Lan cable is fine but no wifi.

Have you tried doing a factory reset ?

Configuration problem -- the IP address for the LAN portion of the router itself could be incorrect. Or the allowed IP address range for client devices such as PCs and Laptops/Notebooks, iPads, Smartphones is not set to match the IP address in your client device. Typical factory Router IP address is 192.168.1.1

Typical device IP address range is 192.168.1.10 to 192.168.50 for home use routers and devices. The configuration software is likely on a CD/DVD. The router configuration can often be accessed by using the browser http:// line ... typically - http://192.168.1.1 - hit enter and go into the router configuration.

Cabling - make sure your CAT5/6 'patch' cable is plugged into the correct port and is snug... With a 5 port Router use ports 2 - 4 .... avoiding ports 1 and 5 just in case these are 'uplink' ports. Make sure you have a standard CAT5/6 'patch' cable and not a crossover cable... Try another cable if you have one.. Most often a port will light up or the number of the port will light up when properly connected - on both ends. If you have long CAT5/6 cables in the walls going to the router or strung under outside eves - then a rodent could have chewed on it. If you are using a CAT5/6 wall jack it could be pinned incorrectly or one wire has come unpinned.

The router configuration info IP address etc. sometimes can be different separately configured for LAN and WiFi.

Router is not an old Zyxel 660 series by the chance?

Sent from my Desire HD using Thaivisa Connect App

If its for a single device could be wired is set to a wrong static ip address and wifi is set to auto ip.

Check your network device internet properties

go start > run type from the command prompt type ipconfig /all post back the results for wireless lan and lan connection

Will just add a little info to the discussion, if I may.

After many months of trouble free service, a similar problem yesterday on TP-Link ADSL router with an attached wired Linksys router (in bridge mode).

Only, one LAN port functioning on the TP-Link? So, only one computer out of six total wired to both routers was networking.

But, wifi good on both routers?

Power off reset, and software restart did not resolve the problem.

Diagnostics (Linux/Windows) indicated invalid starting IP address. Corrupted file?

Reloaded the TP-Link rom file (backup file) via wireless connection. Took about a minute to reload the file. And, another minute for the TP-Link to restart and show login window.

Problem resolved.