Browser cannot connect to sites, but FTP, DNS work fine

[Eitheladar]

I have Windows XP, Home Edition, SP2 installed. Recently I've started having the following problem on all users on that machine:

When I login right after startup, both browsers (IE6 and Firefox 2.0) work fine and show me my home page or whatever other pages I go to.
Then, after a minute or so, both browsers lose connection, as if blocked by a firewall. Firefox brings up the screen "Unable to connect": can't establish a connection to the server at www.google.com , check your computer's network connection, make sure that Firefox is permitted to access the web via your firewall, etc.

After this happens, I can still use ICQ and MSN Messenger. I can open NSLOOKUP and FTP from the command line and access other sites. It's just HTTP access that is blocked.

Can this be the work of a virus? When I click the network connection and ask to "fix" it, it shows no problem. Moreover, it shows traffic coming and going (which makes me worry something is sending out stuff from my computer without my realizing it). But the browsers - dead.

I have Avast! anti-virus up and running, as well as Windows defender. Turning them both off does not help, so it's not them doing the blocking. I ran AdAware and removed all elements it found. I could not obtain Spybot because of this network problem.

I think these problems started shortly after I installed the Cisco VPN client on that machine. I've uninstalled it since, because I thought it was the source of the problem, but the problem has not gone away. I still see a little padlock icon on the larger 'Local Area Connection 5 Status' that I bring up from the Control Panel, so perhaps that could be it?? If it is, how do I remove the effect of the VPN client entirely? Or better yet, how do I get the VPN client to work properly?

To be entirely on the safe side I also ran HijackThis, and am attaching the log.

Any advice or tips on what to look for will be appreciated. I've already read the 'cleaning' thread and acted on it, but it did not help.

Many thanks!

[Teachingmyself]

Have you tried a system restore to the last time you didn't have this problem?

start-programs-accessories-system tools-system restore

[Eitheladar]

Have you tried a system restore to the last time you didn't have this problem?

I hadn't thought of that. I tried it now, but unfortunately all restore points fail. Perhaps this is because I followed the recommended cleaning procedure from these forums and thus destroyed restore information? In any case this is not a viable option for me anymore.

Is there another way to completely remove the effects of the Cisco VPN Client? Maybe the uninstall left something in place anyway.

Alternatively, can anyone see anything suspicious (or not) in the HijackThis log I attached?

[Teachingmyself]

Unfortunately I'm not very experienced in network troubleshooting.

You could try a system repair using you're boot disk but I would seek help to try something else first