|"...the laptop doesn't seem to have any problems connecting to any other networks."|
If you mean via both wired and wireless connections, then there's nothing wrong with your wired and wireless network adapter drivers on the laptop.
High speed modems do not re-set themselves automatically when the internet connection becomes poor and then it becomes better later - the connection will stay poor, even if the led indicating a connection is still lit up.
Sometimes DSL or ADSL connections need to be re-set .
- if the modem or combo router / modem has a switch, switch it off, switch it back on
- if it doesn't have a switch, unplug the AC end of the AC to DC apapter's cord, or unplug the DC cord at the modem or combo router / modem (pull on the plug, NOT THE CORD).
WAIT until all the appropriate leds light up and indicate you have a DSL or ADSL connection.
If the led for the DSL or ADSL connection doesn't light up in a short time, either your ISP is having a problem, or there is too much line noise on your telephone line connection (I frequently have the latter problem).
You can't access the internet from one computer with both a wireless and wired network connection at the same time - it's one or the other. To be sure you're connecting via what you want to, you may need to restart Windows if you change from one to the other.
E.g. disable the wireless adapter, and with the network cable plugged in, restart the computer.
With the wireless adapter enabled, unplug the network cable, restart the computer.
When you have the network cable plugged in, make sure both end connectors are all the way into the network ports. The end connectors should NOT pull out of the network ports until you have pressed the lever on the connectors, and the cable sheath should be clamped inside the end connector, not pulled out of it. The led for that port on the router should light up on the router, at least when the computer is also running and in Windows. The laptop may or may not have an led that lights up at the port.
When you change a setting for a wireless network adapter, the change often does not take affect until after you have restarted the computer.
Wireless network connections are often protected by Security settings in both the wireless adapter's settings and the router's settings by either an encryption code or a password - those must be the same on both ends of the wireless connection, otherwise, you can't connect wirelessly to that router, or if you can, you can connect to it only briefly.
If the Zytel combo router / modem's settings have that code or password set differently that the code or password you're using to access the router wirelessly on your computer, you can't connect to that router wirelessly.
To correct that, you must either
- supply the known correct code or password for the connection to the Zytel that the Zytel requires, in Windows
- or be able to access the router's configuration via another computer that's connected to the Zytel, determine what it's present code or password is, use that code or password in Windows for the wireless connection to the Zytel
- or connect the laptop to the Zytel via a network cable from the laptop and do the same thing
- or connect to the Zytel either way and use the code or password that's being used in Windows for the wireless adapter in the Zytel's configuration.
DSL and ADSL connections have another possibility.
(If your ISP does not require the following, you should have no problem connecting to internet via a network cable connection to the Zytel at any time, unless it needs to be re-set.)
Some DSL and ADSL ISPs require that you register the MAC address of the router or one network adapter on a computer that's connected to the router. That's usually done automatically when you install installation software the ISP has provided, or sometimes you can go to only one specific URL on the web in order to register a MAC address, despite the fact you can't initially access the internet otherwise. Some ISPs allow more than one MAC address be registered, but it's a small number of them , often two.
In that case, the MAC address in all router's configurations for the wired (WAN) connection must be a certain MAC address, or one of a small number of MAC addresses, otherwise you can't connect to the internet.
You can clone the MAC address of one network adapter on a computer when it's the only thing connected to the router, or you can type in a MAC address that you know has been registered in the router's configuration.
E.g. in my case, I use Telus as an ISP, they allow only two MAC addresses to be registered, one is registered when you use their connection installation software, and I initially had a standalone modem connected to a wired network adapter. All my routers must have the same MAC address in their wired configuration as that of the wired network adapter I initially connected to.
If I want to change which MAC address is registered with the ISP, I have to run the ISP's connection installation software again
Obviously, I can't use the default MAC addresses of the routers themselves, unless I use only one router.
You can connect the wireless adapter to only one wireless router at a time. If you want to change which router you connect to wirelessly, you have to select that router's SSID label in Windows and choose to Connect to it.
If the connection says "Security Enabled" the correct code or password must be supplied in order to connect to the router.
Once the correct code or password for a particular connection to a particular router has been supplied, Windows will "remember" that code or password for that router and you don't have to type it again, unless Windows has been reloaded, or you've changed your wireless adapter .
"if I hook up another router to the Zyxel, the laptop now works fine. "
In that case, you must be connecting the ports on the two routers together, and the telephone cable to the other router . In that case, the Zytel is acting as a network switch or a simple network hub. You can access the internet because the settings in the other router's configuration are correct.