PC can see router and other local PCs, but not outside Internet

Frank O · 07 Sep 2011

We have a PC running Windows 7 Home Premium connected to our home network's router via a hardwired LAN connection. The Internet worked fine in the past, but recently has stopped working.

The PC can see our home network's router, and other PCs within the home. However, it can't see the outside Internet.

We booted it in Safe Mode with Networking, and it could see the outside Internet okay. Another time we tried this, however, and it wasn't able to see the outside Internet until we disabled Windows Firewall. Disabling the firewall when Windows is in regular mode does not fix the problem.

Any suggestions on how to proceed? It would be very tedious to go through all the services loaded in regular vs. safe mode. Would it be feasible just to delete the network and let Windows rebuild it from scratch?

Ztruker · 07 Sep 2011

Firewall and Anti-virus can cause this kind of problem. Since you said you already tried disabling the Firewall, try doing so with your AV program.

Another way is as follows:

Maybe something is starting at boot that is causing the problem.

Use msconfig to determine what is causing the problem

These are good tutorials on using msconfig in XP, Vista or Windows 7:
How to use msconfig in Windows XP
How to use msconfig in Windows Vista
How to use msconfig in Windows 7

Click on Start then Run, type msconfig and press Enter.
Click on the Startup tab, record what is currently starting then click the Disable All button.
Reboot and see if it runs better.
If yes then use msconfig to enable several items at a time till you find the culprit.

If no, start msconfig and click on the Services tab.
Check the Hide All Microsoft Services box, record what is currently starting then click the Disable All button.
Again, do a regular boot, see if it runs normal.
If yes then use msconfig to enable services till you find the culprit.

Once you've found the culprit, uninstall it or find out how to eliminate it from your system. Simply disabling it in msconfig is a temporary fix at best.
Enable everything else you disabled.

LTFUbar · 07 Sep 2011

DNS hijacked?

If your computer can see the router (EG 192.168.1.1)

Can you computer see an outside ip? like 74.86.171.210

Click on "Start"

Type "cmd"

Press "ENTER"

Type "ping 74.86.171.210"

Press "ENTER"

If so the problem just might be a virus.

Use Malwarebytes AntiMalware to check

Frank O · 07 Sep 2011

Thanks, all good ideas.

I forgot to mention that we had already run Malwarebytes and Spybot Search & Destroy, both of which came up clean.

We disabled Windows Firewall and uninstalled Avast anti-virus, after which we found the PC was able to access the Internet fine in normal mode in Windows. We then reenabled Windows Firewall, and after an hour or so it still seems to be behaving normally. As a next step, we will probably reinstall Avast and see how things work. If a problem occurs then, I guess we would need to decide between trying to work it out with Avast vs. trying another AV program.

Ztruker · 08 Sep 2011

I would suggest not installing Avast but installing Microsoft Security Essentials instead.

Frank O · 08 Sep 2011

We've used various anti-virus programs over the years. Eventually, many have disappointed us because (a) over time (for example, when a rewritten version comes out), they create a detectable performance hit, and/or (b) they don't catch enough.

How do you feel Microsoft Security Essentials rates on these two criteria?

Ztruker · 08 Sep 2011

Excellent for both. It's not a suite, strictly an anti-virus program. It does that very well for me. I also run Malware Bytes Anti Malware Pro for Spyware and browser protection.

Frank O · 08 Sep 2011

An update:

We discovered that Microsoft Security Essentials was already installed and running on this PC. We didn't do this intentionally, so we wonder if it could have been installed and activated by Windows Updates?

In any event, this probably explains why installing and running Avast caused problems.

Anyway, thanks again for the various suggestions on debugging this problem.

Golden · 08 Sep 2011

Yep, the conflict between the two security software would cause this Frank. Good pick-up.

As far as I am aware MSE will not self-install - can you check in the Control Panel\Programs\Programs and Features area as it would show the date that MSE was installed? That might help you if you want to determine how/why/when it was installed.

Regards,
Golden