Trouble connecting to Network/Internet

This is my first post and I am no computer pro, but as the owner of a small business on a tight budget, it is up to me to fix problems as they come up on our 4 Dell computer network.

 

We have 3 Desktops - Dimension 8200, Dimension 3000, and Dimension E520 also have an Inspirion 8600 that connects to the network wirelessly. The computers were added one by one as the company grew. I had to learn on the job...

 

I have all of the computers on a network - I have a Westell Wirespeed Modem Model B90 and a Dell Wireless Router Model WRTA 108GD I have all three desktops plugged directly into the back of the Wireless Router and the laptop connect wirelessly. We have DSL, so the phone cord goes from the Westell to the special phone jack.

 

Here is the problem, a few days ago I downloaded a software update onto my main computer. All went well. I downloaded the same software onto the Dimension E520 and while it was in the process of downloading, I got a message from my front page toolbar that popped up and said "A Network cable is unplugged" I had changed nothing.

 

The main computer is now unable to connect to the internet or the network, but all the other computers can connect to the internet and the network (with each other but not with the main computer). The other computers cannot, however, connect to the network printers - I believe because they all go through the main computer.

 

Now, I have done everything I can think to do -unplugged the modem and router and plugged them back in, multiple times. Reset both of them pushing the little button in the back. Did a system restore (a few times) checked the cables by connecting directly to the modem and I was able to connect to the internet with the main computer (so the cords are all working). I did have to re set up the internet connection in the main computer each time I plugged the ethernet cable directly into the Modem.

 

The network problem is occuring I think because the network cannot renew the ip address. I have the ip address and have done a ping to it and I get 4 packets sent and 4 packets received. So I think that is good news....but that is where I get fuzzy and really need help to get this back up and running.

 

Can't pay my bills until I get it fixed....thanks for any help you can give me.