How to use a 2Wire 2701HG-B as a router only

If you try the other things suggested by @MaQleod and @Matth1a3 and it really does seem that the wifi connection is the issue, it may be that some other device/s nearby are suddenly transmitting on frequencies, or just generating interference, on or near your wifi channel frequency during the time you are having the problem.

Things might improve or get worse if you change transmitting channel and it may help if you can run an app that lets you know what wireless activity is happening around the time you have problems; if you are running Widows, you could try something like Netstumbler or Meraki WiFi Stumbler

Things that may cause interference include:

• Fluorescent (CFL) lamps (is a security light coming on outside?)
• Nearby domestic devices using cheaper overnight electricity (eg: washing machines or storage heaters)
• Someone scheduling downloads during their broadband 'off peak' period

The one thing that kills my wifi is my 2.4GHz video sender - it's set on its channel 3 and everything works fine, but if I have a power cut (my house is in a small village in the middle of the countryside and we have the odd power fluctuation a few times a year) and it resets itself to its channel 1 then I can connect to my wifi but no data gets sent or received (it's a good 'power fail indicator!!'). Maybe someone locally switches on a video sender and watches late night TV? Again, changing your wifi channel may help.

You should also consider the possibility that someone has managed to hook up to your wifi network and is using your bandwidth for some heavy downloads, causing difficulties for other devices, so it might be an idea to check that you are using strong wifi encryption (WPA or WPA2) and change your password to something 'stronger'/longer - maybe something of 12 characters or more with a combination of letters and numbers.

I'd been puzzling over how you could get it to work, when I remembered Connectify. If you can get your hands on a wireless USB it should work perfectly for your situation instead of having to deal with that router.

I'm not sure there's a good way to connect the router like that, there's too many variables between the Siemens device and the cable modem. You might be able to connect the cable modem to a LAN port in the router, shut off DHCP in the router, give the router a static IP that's on the same subnet as the modem but not taking the modem's IP, and see if it will route packets appropriately between your computer and the cable modem. If you don't even get DHCP from the cable modem, that's a bad sign. You could try setting a static IP address for your computer and manually assigning the cable modem as the gateway, but it might just ignore your PC if it doesn't go through DHCP first (I know mine does.) The router might get confused too if it's looking for WAN, so setting to bridged mode might help. It all really depends on how the cable modem and router operate, and I'm not sure how much of this is standards based. Might end up being a lot of trial and error...

Connectify though is really easy, but you'll need XP with SP3, and you'll want to run in Ad-hoc mode anyway.