My desktop says I don't have a "valid IP configuration"

I just bought a new router today after my last one went kaput.

The router I purchased was the Netgear R6250, and after setting it up, I tested it on every device on that level of my house and they all worked just fine.
But, I went up to my office and my desktop couldn't connect to the internet through my hardwired (Cat 5) connection like it used to be able to do.

I did a little troubleshooting and Windows says:
"Local Area Connection" doesn't have a valid IP configuration
and it says that it wasn't fixed.

I call Netgear only to find out that my "Free 90 day tech support" was a sham and that my router and my desktop apparently were not communicating at all.
They did have me run ipconfig through the command line on my desktop, and told me that my IPv4 address of "169.254.170.50" was an invalid one.

I'm not sure really what to do, but I do need my hardwired connection, the wireless usb card I have in my desktop can't even get 1mbps.

Let me know if there is any more information you need to help me, and I'll be happy to provide it.

Hi ZBee,

Your problem indicates that your PC is unable to obtain an IP address and subnet mask from your Netgear R6250. Thus, it uses APIPA (Automatic Private IP Addressing) a feature in Windows to automatically configure itself with an IP address and subnet mask when a DHCP server isn't available. The IP address range is 169.254.0.1 through 169.254.255.254, a range that has been reserved especially for Microsoft.

Assuming that your PC is properly wired/connected to your router, please make sure that the DHCP client service is started and set to automatic (under Control Panel\Administrative Tool\Services) and try to restart your PC after doing so.

Alright, I made sure that was set to automatic and I restarted it, but I had the exact same issue still.
Nothing changed.

Not intentionally, but yes, now that I think about it I have turned them off in that order. I'm not sure that the router fully booted because it's lights are a bit confusing to me, but by the time I turned it on then walked all the way up stairs it probably had.

The cord connecting the router to the cable switch is the 2nd farthest from the Internet In (WAN?) port, actually.

Comcast -> Modem -> Router -> Ethernet Switch -> Desktop

Before I got this new router, it was working absolutely wonderfully at an average of 55mbps, and that's about what I got on my roommate's desktop just a minute ago when I tested that.