Question : Problem: Can't get online! Airport/Network/Mac problems!

We have a DSL modem connected with a short cord directly to the phone jack. We have 2 Airport Express routers, a newer one (6 months) plugged into the outlet near the modem and connected to the modem and the older one (18 months) plugged into an outlet at the top of a staircase in  an effort to boost the signal. We had it up and running for about 3 months but now I cannot get the newer computer (18 month-Mac G5 desktop) to create a network. We have an older computer (3-yr old Mac G-5 desktop) and several IBM laptops that also need internet access. I have reset the routers but it may be that I have not followed the right order, in any case it is driving me crazy because I can almost understand what the problem is but not quite.

Answer : Problem: Can't get online! Airport/Network/Mac problems!

Have you tried plugging a computer into the ethernet port of the newer Airport and run the Airport utility to make sure it's still configured properly?

If you have or if it is, I"d next check and encryption you have enabled such as WPA2 to make sure that the key hasn't become corrupt.  In other words reenter the key/pass-phrase on the airport and on the computers. If you are using encryption, try temporarily removing it and see if the computers can connect.