Cable modem connection keeps repeating checking and then down over and over, tried a different router works fine, tried a different modem same issue

The speed of your internet is determined by your service provider and their modem. If possible, connect directly to the modem to check the speed. If you suspect you D-Link router is not allowing you to get full internet speed, first a Hard Reboot of you Router and Modem.
If that did not solve the issue, try a known working LAN 5e cable between your modem and router. After you have established it is not a cable issue, do a factory reset.
I had an issue where my speed to the internet modem was fine, but the router LAN connections only provide a faction of the internet speed. After testing cables, etc I did a factory reset and it restored full connection speed on my router LAN ports.

Since the wireless works fine on your router, then it is possible that there is a problem either on your ethernet cable or on the port of the belkin router.
Try a different ethernet cable. (Ethernet cable is the one that is connected from your computer to the router.) If you don't have a spare cable, you can directly connect the computer to the modem, just to isolate the issue and determine if it is the cable or the computer itself.
If you have determined that the cable is working fine, then try a different port on the router.
I hope this helps!

Here are a few simple things to check:
If your PC is connected via wireless:
- Make sure you didn't go out of signal range
If your PC is connected via wired cable:
- Make sure the cable is secured into your router
If both check out:
- Check the cable between your router and internet modem.
If all connections are solid:
- Try using a different cable from the PC to the router, and from the router to your internet modem. Cables can go bad, and a new one could be an easy fix.
If all else fails, you may have experienced an intermitted connection issue:
- Try unplugging your internet modem and router for 30 seconds, then plug in your internet modem first and after 60 seconds plug in your router.
- Try restarting your PC

If none of those work, contact your Internet Service Provider.

If the modem light keeps blinking, it means that the router hasn't been configured yet. Also, rarely, it can be an issue with WAN port/modem port on the router or the ethernet cable connecting the modem to router or finally, modem may not be working as its not applicable in this case(as you said).
How to configure the router for Time Warner?
1.Connect comp.--(gray port) router (yellow port)--modem
2.On the computer, open the router page by typing 192.168.2.1 in the address bar of browser
3.Under Internet Settings, change the connection type as Dynamic.
4.On the far left column, click on "MAC address" under Internet WAN.
5.Click on clone and apply changes and finally check Internet status
6.If internet status > Not connected, we need to do a network power cycle
7.For this, unplug the power from router, then from modem, then unplug the coaxial cable from cable modem.
8. Wait for 10 sec, then connect the coaxial cable, then connect power to modem, wait for lights on modem to get steady, then finally, plug in the power to router.
Now, you may see proper lights lit on the router.
All my best wishes for a fast internet service through the router.

For any advanced help, revert asap!
Thanks and regards,
Arvind

If you have a Cable Modem try doing a MAC cloning on the router and check the Firmware update, if you have a DSL connection try changing the LAN ip Address (Eg:- from 192.168.1.1 to 192.168.2.1) or if you have PPPOE then use the correct PPPOE username and password on the router and try to set it up, if that dosent work then we will take it from that point.

From the laptop try pinging the router IP and then try to ping 4.2.2.2 or yahoo.com or google.com if you get replies the internet connection is fine and your router is connected to internet

As the issue is with 2 different devices it seems that issue is with router's internet connections, also connect the laptop with a cable and check the internet connection if that works fine issue is with the wireless security settings of the router

The user guide of your router is in the link below

http://www.scribd.com/doc/10510222/Netcomm-NB5Plus4W-Modem-User-Guide

Let me know if this help

Regards

Regards

This is a fairly simple thing to trouble shoot. If you are losing your wireless signal where your OS tells you that you have been disconnected from the wireless network then there is an issue with your wireless router. If your cable modem drops the data link to your ISP your wireless network will still work 100% fine, however websites will not load, but the router admin page should.

The end all be all way to prove it is not your wireless router is to simply use a network cable for a few days and see if you get the same issues. If it does turn out to be your wireless router there could be an issue with interference and I would recommend trying a different wireless channel.

I would have to say this is a problem with Comcast, call them and ask for a line test, tell them that you are having this problem on multiple computers, and you have even tried connecting directly to the modem. If they can run a test on the line, hopefully that will shed some light on the issue.

Often times with Cable/Phone companies, the right hand doesn't know what the left is doing, be instant that they check, at the very least they can check connection to your modem from their end.

looks like a common issue on routers and cable modem, well a little common.

the power comming fromt he modem (information pass) is too much for the internet port on the router to handle that it quits if the surge from the modem comes.

here is what you do:

get a longer ethernet cable to connect your modem and the router, may 10-15 feet ethernet cable, put it in a coil and tie a knot in the middle, just look at the picture below.

once this is done, you may access the router's page again and make sure that the MAC clone feature is enabled and perform a power cycle. power down the modem and the router, power up the modem first, wait for around a minute or until the ONLINE light is steady and then turn the router on. after that try your connection on the router.