Can't Connect To DNS Or Ping But Get IP From DHCP

My parents Windows 7 PC has suddenly stopped being able to connect to the Internet. Using the "Diagnose problem" feature in the Manage Network Interfaces panel results in a message claiming that it cannot reach the DNS server and that the connection needs to be reset. Doing so has no effect. It is connected to a DSL router via an ethernet cable.The NIC is set to dynamically receive its IP and DNS settings via DHCP which it obtains from the DSL router. Executing ipconfig from a DOS prompt shows that this is occurring as expected, with an assigned IP of 192.168.2.10. The gateway and dns are set to the IP address of the router, which is 192.168.2.1. Note that I can't even ping the router at 192.168.2.1.I also tried static settings in the available range and tried using open DNS IP addresses.

They also have a laptop which connects to the same router wirelessly using DHCP and it is working fine. Using this laptop, I can log into the router and see both it and the problem PC in the list of connected devices, each with the dynamically assigned IP addresses as seen using ipconfig on each. Unplugging the ethernet cable shows the connection status changing in the list of connected devices in the router. From the laptop, I can ping the router and running ipconfig shows that it obtains the same gateway and dns as the PC and the next available IP - 1292.168.2.11.So this leads me to believe the following:

1- The router, NIC and cat 5 ethernet cable are working fine at the hardware level.

2- The DNS settings in the router are fine, as the laptop works

Perhaps coincidentally, the same day it stopped working they received one of those bogus "This is Microsoft calling" calls claiming their PC was infected, but they had heard of the scam and hung up. Naturally, I started suspecting a virus, but a full system scan using McAffee produced nothing. If it was a DNS changing virus, would I not still be able to ping the router using the IP address?