Help me troubleshoot my internet connection (not spyware)

Factual Questions
1

Three computers in the house: a “main” PC; alternate PC and a laptop. All are running Windows XP. I have a cable modem and Linksys wireless router. My “main” PC was cabled directly into the router; other PCs in the house used their wireless cards or wireless adapters. Everything was just dandy…then yesterday, the main PC was unable to connect–click on the Internet Explorer icon just hangs.

Here’s what I’ve tried:

Plug (ethernet cable) main PC directly into modem: works.
Add a USB wireless adapter to main PC: wireless network connection looks good (from the Network Connections status screen), but no connection.
Other wireless connections in the house (laptop and alternate PC): continue to work.
System restore to a date last week: no effect.

So it looks like the main PC has lost the ability to communicate with the router, although the other PCs in the house can talk just fine.

Anyone? Anyone?

2

Have a look at the properties of the TCP protocol in your Network Properties dialog; is it set up to obtain an IP address and DNS automatically? (it probably should be). Is it set up to use a proxy server? (it probably shouldn’t be, except perhaps 'automatic detection of proxy - this is in ‘LAN Settings’, within the connection tab of the properties dialog for IE).

3

Thanks, mangetout–It may be a while (until I get home from work) before I can try your suggestion. Just another thing to add: the problem may have started when I was installing Tivo’s home network software. A dialog box popped up, saying that Tivo needed to fiddle with my IP/internet/firewall settings…OK? Should’ve triggered an alarm right there…