Pages Not Found

["Ex Arca" <exarca@msn.com>]

Server has been working fine for past year.  In recent days though, maybe 
25% of time, I get this error:

"The page cannot be displayed"

But if I wait a few minutes, then it works again.

I'm a programmer, but not a network guru, so I don't even know where to 
begin looking to find out what the problem is.

Can someone point me in the right direction?  Like is there some diagnostic 
tool I can run on the server or the user's machine?

Any help appreciated.

 --Anna


Server setup:

Apache->Debian->Linksys->Cablemodem->ISP