You have two issues:
If DD-WRT is acting as a repeater, then it doesn't have an IP - it's just taking traffic in one end and spitting it back out the other like a switch or an Ethernet cable.
A cable modem will respond to one and only one device that appears on its Ethernet port - typically the first one. If you try to connect a switch to a cable modem, it will only talk to the first device that talks to it. If you want to share your cable modem's Internet among multiple systems, that one device needs to be a router.
If your PC can get Internet via the cable modem which it sounds like it already does, basically your solution is to turn the PC into a router. If this PC is running Windows, the Internet Connection Sharing feature pretty much does this and will take care of DHCP for you as well.
Routers require two network interfaces - one for the cable modem or WAN, and the other for your LAN. The problem with using your wireless USB as the "LAN" side is that it has to work like an AP if you want more than one system to connect to it. AP mode is probably not supported by your hardware.
But you could get a USB-to-Ethernet adapter, and a second wireless router. Set up Internet Connection Sharing on the adapter, and disable DHCP on the second wireless router (because Internet Connection Sharing will provide the DHCP on the PC) and connect a LAN port of your second wireless router (NOT the WAN or Internet port) to the USB-to-Ethernet adapter and it will work.
How does your computer get an IP if there's no DHCP? Can you not just turn on DHCP on the DD-WRT router? – qasdfdsaq – 2015-10-21T20:27:23.263
I haven't a clue how it gets an IP. It does, I am online through the DD-WRT now on my PC. I have no access to the DD-WRT settings (don't have the password, landlords have their guy who gets paid 40 bucks per visit, and he has been here today, and screwed this up). As I see it, only one person at a time can have Internet connection through this DD-WRT device, others connect, but can't acess internet. Here is the screenshot of what I can acess. [link] http://imgur.com/6Y1MU4y @qasdfdsaq
– user22975 – 2015-10-21T20:30:05.110so, ({house}---wire---{ddwrt device}:::wireless:::) is broken, but ({house}---wire---{ddwrt device}---wire---pc) works? – Yorik – 2015-10-21T20:36:48.277
@Yorik its house ---wire--- some TP LINK ---wireless--- DD-WRT ---wire--- My PC and yes that one works, but the DD-WRT ---wireless-- laptop doesnt. And I've just connected another laptop with a cable while my main PC is online and that doesn't work either. – user22975 – 2015-10-21T20:38:39.503
Are you running Windows? If so do
ipconfig /allin a cmd prompt. Your screenshot is helpful. It shows DHCP is off, but nothing preventing other computers from connecting. It is operating in full router mode. I suspect simply replicating an appropriate static IP setting from your computer on another would work – qasdfdsaq – 2015-10-21T21:32:55.387@qasdfsaq I have set static IP addresses on two diffetent machines and it works. Also without imputing DNS addresses web browsing didn't work. Now I would still like to share the connection from my PC via wireless and have done so with remote router program but the speeds are really low and it disconnects my main PC when the connected device starts using the connection. – user22975 – 2015-10-22T09:34:35.333