Can I have 2 ADSL modems working together?

At the moment, I have a wired ADSL modem going into my main BT socket. I've also got an older computer up in the spare room near an extension socket & I've now another ADSL modem. If I installed that on the old computer & plugged into the extension socket, does anyone know if I could have both computers on at the same time accessing the internet? Or if ever I wanted to use the one in the spare room, would I have to turn off the main one down here by the BT socket?

That will not work.

What you need to do is use an ADSL modem/router e.g something like a Netgear DGN2200 to share the connection over Ethernet or wireless.

What is the make and model of the ADSL modems you have?

You cannot connect two modems at the same time.

Do you mean modems, or modem/routers (usually just called routers for bevity)? Are you running Windows on the two PCs?

If you have a modem/router then that can service more than one computer, either by wired ethernet or by wireless links. That's what routers do. If it doesn't have built-in wireless you can connect a WAP, (Wireless Access Point), to it. Either or both computers can be on and accessing the internet.

If you truly have just a modem, and are running Windows, you can still share the connection with Windows Connection Sharing. That would need an ethernet cable running between the two computers - maximum cable length 100 metres. For that to work, the computer connected to the modem needs to be on in order for the other to work.

Alternatively, if you can't conveniently run that cable, you can use Powerline Adadpters. There are a few makes.

Further to the other comments. If you do have both connected and just turn on te one you want, you will still have problems. You neeed to actually disconnect the unused modem before turning the other on.

Not forgetting setting a second router as a slave to the master ADSL router.

Thank you, the one I've been using down here is a Sitecom DC227 and it's simply described as on the box an ADSL2+ modem. The other I've just bought was cheap, that is a TP-Link TD-8817 and is described as an ADSL2+ Ethernet/USB Modem Router. I don't want to run any cable & it's only for emergencies using the telephone extension cable so your real message is I must always have one turned off and completely disconnected from the BT socket as well - that's right isn't it? Thanks to everyone for their advice

Both of those devices are wired routers with built in modems.
So yes, you can unplug one and use another.

If you ever decide you want wireless, then add a wireless access point to either of those two devices.

Thank you for your reply, when you say "add a wireless access point to either of those two devices" I don't quite understand what you mean? I don't have a wireless card in either of my PCs so presume I'd need that, also wouldn't I need a hub or something from BT - sorry as you can see I'm not too clued up on broadband. I do appreciate your help though

As you have no wireless devices, then this is really just for the future if you were to buy a phone/tablet or other wireless device.

I'd use the TP-Link as the main ADSL modem/router and buy something like to create the wireless signal
http://www.amazon.co.uk/gp/product/B002YETVVE/ref=as...

There is nothing stopping you continuing to use Ethernet for your existing computers. Adding the wireless access point just gives you the extra option of wireless.

There is no need for anything from BT, you can buy all you need from places like Amazon.

That's very helpful thanks, so if my main PC had a wireless card installed you are saying all I would need is that TP-Link-TL that you kindly included in that link from Amazon & I would then have wireless - and if my other old PC had a wireless card as well that would receive wireless without needing the other modem at all? Have I understood you correctly there? Thanks