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One PC on my network cannot ping anything. Here is the relevant troubleshooting information I've been able to gather so far:

  1. Windows firewall is off on this PC.
  2. It CAN resolve DNS to obtain IP addresses, and it can't ping direct IP addresses either.
  3. Other PC's on the network CAN ping the same websites correctly.
  4. It can browse websites using Chrome, IE, and Firefox just fine.
  5. Certain applications can access information and some cannot.
  6. My host files have not been tampered with. They have no strange settings.
  7. This happened right after I installed some questionable software that I downloaded.
  8. Windows 7 64 bit PC with ample specs for just about anything.
  9. Not on a Doman, no proxy server, tried setting DNS to google's DNS.
  10. Tracert returns absolutely nothing. The trace route never leaves the computer.
  11. Direct hard-wired to router.

My immediate suspicion is that the questionable software mentioned in 7 contained some sort of malware that is monitoring or blocking TCP/IP calls unless they're from particular software, and I should probably just wipe this machine and start from scratch.

Does anyone have any other suggestions for troubleshooting that may help me diagnose it? or just outright fixes of course... one of those would be wonderful right now.

Remember: Not a DNS issue, not an ISP issue, not a firewall issue, not a host file issue.

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    Are the "other PCs" also "hard-wired" to the same router? Can you ping the router? Dec 20 '15 at 5:32
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    I should probably just wipe this machine and start from scratch - Yes you should.
    – joeqwerty
    Dec 20 '15 at 6:13
  • @ringø Yes, the other PCs are hard-wired to the router, and no this PC cannot ping the router.
    – Jrud
    Dec 20 '15 at 7:08
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Firstly, ping isn't TCP, it's ICMP. It's not unusual (though bad practice) to find a firewall that blocks ICMP, which still leaves most other things working. I see that you say windows firewall is disabled, but maybe you can look at traffic on the network and see if pings are failing to go out, or failing to get back. tracert also uses ICMP by default, although there are related techniques that use TCP.

Maybe check your routing table, and access to local services on the network (e.g. http on your router?) just in case there's some sort of network tunnelling involved that you're not aware of (not something I've heard of malware doing, but check anyway).

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  • Blah, you can tell I don't have any formal training in networking. I am a software developer who unfortunately has to troubleshoot networking sometimes. There is nothing in the router's routing tables. Looking through the router's Service & Website blocking sections has no results either. HTTP on port forwarding is directed to the 2nd PC that can ping out, but it's been set that way for years, and this is a recent issue.
    – Jrud
    Dec 20 '15 at 7:15
  • I meant look at the routing tables on the PC, in case the default route is being tunnelled through a VPN or similar. I'm not much of a windows user, but I think it's just route print from a command shell.
    – mc0e
    Dec 20 '15 at 17:37
  • Can you ping the problematic PC from another host on your network?
    – mc0e
    Dec 20 '15 at 17:37
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First, I would double check that the firewall is completely disabled on the PC.

Also, ensure some other malware-protection programs or other "benevolent" software are not preventing your PC from having ping work: answering a ping is seen as a security weakness (as the answerer says "yes, this is a valid IP"), and, if indeed such a software is in effect, it may also filter out all ICMPs including the answers (voluntarily or by mistake).

Now, on Windows 7 there are many pages explaining how to start the OS in "safe mode" with networking, like this one. You may want to try this, if that prevents the malware - if any - to run.

And finally, in the same register, try malware detection - but I guess you did this already.

Besides,

networking issues may have many many sources.

  • you may have a routing issue, for instance if wireless is also available and configured, and, for some reasons, some protocols/applications go for the wifi interface - while the browsers selects the wired interface instead... (disable wireless / any other interfaces just in case - if available)

  • try to run a query in curl or wget (or similar) from a prompt DOS window, that bypasses the browser,

  • ensure the "other PCs" don't have a specific configuration at the router level that allows ping (...) to come and go / if this PC doesn't have a special setup at the router level

  • replace the cable - that'd be strange that some sites are browsable via TCP, and ICMP doesn't, but you never know (TCP is "reliable", meaning it will try a few times before giving up)

  • check the BIOS settings for any unsolicited "protection" setup especially at the NIC level

  • create a bootable Ubuntu USB stick boot on the stick and access the console (or gparted live probably faster, and gives access to console). If Linux can ping, this is a Windows specific issue.

  • check the forums for the NIC brand/type for any strangeness related to Windows 7

A lot of assumptions here, but when it comes to network issues, the scope of possibilities is high!

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