Linksys router - not all pc's accessing the internet

My friend has a wireless Linksys router at home with 3 pc’s networked (the main pc with 2 others networked), OS windows XP. Everything was working fine until they ran the Trend antivirus software and deleted many files that Trend said were viruses or not needed (could they have deleted the ip address of one of the computers?).

Now, they can use the main computer to access the internet but the other 2 computers can not access the internet or the other 2 computers will work on the internet but the main computer will not access the internet. Does anyone have any idea how to fix this?

Thank you for any help you may have.

:)