Internet Connection Has Deteriorated On The Computer

My computer is connected through the internet through a router and dsl modem which have worked in the past.During the past two days the internet connection has deteriorated on the XP computer but has stayed the same for the win98 computer eliminating suspicion from the isp.Downloading files for updates, logging into websites etc. is not working unless connected directly to the internet through the modem and sometimes that doesn't even work.I tried running the Norton Anti-Virus scanner but it said it was missing components and when I tried to reinstall the installation failed. I was luckily able to download a free scanner from the internet and ran it on reboot and found 53 various Trojan files infecting to be what i thought useless files. After the scan and deletion the internet still does not work.The problem is i can't repair internet explorer because everything on XP is integrated with the internet and getting updates from the internet is impossible, even system file checker doesn't work without access to the internet.A viable culprit in my mind would be the Norton Internet Security program that comes along with Norton Anti-Virus, which changed internet settings on installation and in the past would not allow the internet to work without it at least on and disabled.I am also missing the .dll files iecont and iecontlc.