Dell Optiplex 990 ethernet stops working

@ShyGuy1 thanks for getting in touch. Your system not having a valid IP configuration could be a result of corrupt network settings, a failed router or a faulty network card on the system.

You have stated tt you have tried restarting your system multiple times and it failed to fix the issue.

a) Did you also try restarting your router / modem?

b) When was the system last working?

c) Do you have any other systems connected to the router?

d) Have you tried disconnecting the network cable from the tower and then reconnecting it?

e) Are both lights lit up on the network port on the tower (One should be constant orange to indicate a connection, the other should be flashing green, yellow or orange to indicate transfer speed) ?

If the hardware is working fine, I would suggest renewing your internet connection settings. I would recommend following through the section titled "Resetting network connections" from this third party non Dell website - https://appuals.com/ethernet-doesnt-have-a-valid-ip-configuration/

I look forward to hearing how you get on.

Alan

DHCP server is required.

Cable Should be CAT5 or CAT6

Cat 3 cables will not connect because they do not meet minimum spec for 100 meg to 1 Gig ethernet.

Pairs must be used in cables but sometimes people wire them straight thru instead of 1 2 3 6

No on the ethernet port its only lighting up yellow. The internet was working perfectly fine up until a couple of days ago. My pc is the only thing I have plugged in right now to my router via ethernet 

I tried following all the steps in the video but none of them worked 

@ShyGuy1 did you try restarting the router?

Did you try disconnecting and reconnecting the network cable to the tower?

For the link I provided, it was the instructions for resetting the network you needed to try rather than the steps in the video, these ones

Here's the link again https://appuals.com/ethernet-doesnt-have-a-valid-ip-configuration/

Alan

Yes I tried replugging the cable and resetting my router. I've tried 3 different cables and none of them worked. I tried running those commands too but I had no luck with it. 

@ShyGuy1 that ultimately leads to the OS being at fault. Depending on what version of the operating system you have installed you may be able to do a system restore to a previous point when the system was working fine, if you are running on Windows 7.

You may also want to try reinstalling the network driver to see if that resolves the issue - https://www.dell.com/support/home/us/en/04/drivers/driversdetails?driverid=nngmh&oscode=w764&productcode=optiplex-990

As a final resort you could try a repair install on the operating system and ultimately if that fails to resolve the issue I would be looking at a clean install of Windows.

Alan