This is a weird one....to me anyway.
I have a client with a Windows 7 PC. Starting three days ago, he suddenly could no longer access the Internet. He has just the PC which is connected to a Cisco/Linksys wireless router. The computer is getting an IP address from the router. When I try to ping the router I get two replies from the IP address of the computer with the message, "Destination host unreachable" and two "Request time out."
I tested the router with a different computer and it works fine. Tried both a hard wire and wireless connection, same result. Uninstalled both adapters in device manager and re-booted; same result. Tried resetting the IP stack and tried a suggestion that had me create a new DWord entry named "ArpRetryCount" in HKLM\System\CurrentControlSet\Services\Tcpip\Parameters. No joy.
I've tried the system in Safe Mode, did a System Restore to before the problem started, scanned for spyware, cleaned up temp files. I am at a loss as what to try next short of doing a Windows repair install.