D-link router power light is red - D-Link ADSL2/2+ Modem/Wireless Router 4-Port Switch, 802.11g, QoS (DSL-2640B)

Reset router. There are two resets. A simple push reboots and holding it in clears all custom settings. Try the first.

This is a quick fix and usually does it. Test with network cable and work your way backwards to modem if you still have problems.

If the power light is red this is a system error.

Try to reset the router by holding and pressing the reset button for 10 seconds. Then power cycle the router.

If the power light is still red. It is possible that the router is already defective.

Please make sure that the router is properly configured then only the internet light will be green

Talk to your ISP regarding the router configuration

I have same problem. I was able to manually assign IP of 192.168.1.2 and was able to connect to 192.168.1.1 (the d-link) but it keeps asking for Factory Supplied Firmware From ISP. I flash it with the firmware but then it crashes again.

You said there is a diag light lit up on the router.
In that case you can try to reset the rotuer for 30seconds . unplug the power and plug it back in. wait for a minute.
Check the lights on the rotuer. If you still see the diag light then try to reset the rotuer again. If there is a diag light on the router then the rotuer is not working.
Try to reset the rotuer for 2 - 3 times . power cycle the router till you get no diag light.
Once the diag light is gone then reconfigure the router.
Connect the modem to WAN port and computer to one of the 4 ports. Do not conenct anything to the uplink port.
Reconfigure the router.
Click Here to know more about how to set up router

1st: Have you paid your bill?
2nd: Have you power cycled?
Full Power Cycle is as follows:

Turn off all components plugged into the router(Computers, Printers, etc.) Unplug the power from the router. Unplug the data cable(DSL, Coax) going TO the router. Wait aprox. 1 minute. Plug data cable and power cable back into router. Wait about 1 minute. Turn computers back on. Problem Solved?

If not and you're using DSL make sure all DSL filters are in place and that none have come undone. Make sure the phone line is still plugged in. Problem Solved?

If not contact your ISP and ask if they are doing any maintenance in your area that may by effecting your service. Ask them to perform a line test on you. If all else fails ask them to have a technician come out and help solve the issue.

dsl2640b router power light shows red but should be green

Hi! before u buy a router try to press the reset button on the back of the router for 10sec, the power of the router shud be on and after that unplug it for 15secs.. then plug it back in..if there is no change on the lights try to download the firmware of your router from dlink website.. this will fix the concern but if not then this is the time that u have to buy a new router.. try this possible option first.. sometimes the firmware from the router is corrupted..

Try another power adapter.

Hi

Flashing red light means system restarted due to power outage and or system was restarted, Wait for system to boot. The power adapter may not be connected firmly in the power socket or the wire connected at the back of your router may be loose.

Please do accept this solution and revert for further assistance.

Thanks
Rylee