D-Link not connecting to work!!

I have a D-Link DI-634M wireless router. Up until now, for almost 3 months, I was able to connect to my work through an application X(proprietary) provided by my employer. Suddenly, for last couple of days, I cannot connect. The error message I get is: "The remote host is not responding". I am using DSL. I have tried the following:

1)I have connected the DSL modem directly to the computer. This way I CAN connect to my work using application X just like before.
2)I have shut down the computer, powered off the DSL modem and the router and restarted everything in this sequence:
computer, DSL modem, router. I still CANNOT connect.
3)I have tried switching port from 1 to 2 and then 1 to 4 in the router. Still CANNOT connect.

Configuration Info:
1)OS: Windows XP SP2

Absolutely, nothing has changed 2 days ago. No software was installed. No hardware was added. Any ideas?
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PUNKYConnect With a Mentor Commented:
I understand your question, but right now we are trying to find what is wrong, the router or the PC. If router, you could get other to replace, if from PC we would need more infor about that.

Hook up PC directly to DSL modem, if you can access internet, then modem and your dsl are OK.
Hook up PC with router only and see if connection made between PC and router.

Just about step by step to narrow down issue.
Have you tried reset router yet? if not, try that.
soccerplayerAuthor Commented:
Yes. That's what is in #2.
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What protocol (TCP, UDP) and ports does it use?  Could your ISP have started blocking that port.
soccerplayerAuthor Commented:
How can I tell the protocol? What is UDP? On the router, I have 4 ports, 1,2,3,4. Are these the ports that you are talking about?
Can you open the page or ? If not, there is no communicate between computer to router. Then, issue might be from computers (winsock, incorrect settings, etc.).

Reset router to factory default is what I meant. Turn off firewall, no WEP, WAP, only SSID. Let all settings are default and try connect it see if works.
soccerplayerAuthor Commented:
I can connect to the internet through the router. It is my work machine that I cannot connect to through application X as mentioned above.
soccerplayerAuthor Commented:
I don't think it is the PC because, from this same PC, I CAN connect to my work computer using the DSL modem directly. It is when I go through the router that I am having problems and that is also for last 2 days. I can also connect to the internet with just the DSL and with the DSL and the router.

I would suggest going with Punky's suggestion.  Reset is different than rebooting.  A reset is when you reset the router back to factory defaults.  Usually there is a small hole you need to use a paperclip to reset the router with.  Dlinks usually require that you unplug the power to the router, press and hold the button for 10 seconds.  Then you will need to log back into the router and reconfigure the correct settings.

Now, if it still doesn't connect, we will have to determine what sort of traffic the program is attempting to use.  Wireshark (AKA Ethereal) is a great tool to use for this.  Once you determine the port number and traffic type (UDP,TCP), then you can contact your ISP and find out if they are blocking them on the network.  It may be a good idea to contact the helpdesk at your organization to find out what protocol and port number the application is using.
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