To solve this problem, the user needs to have basic knowledge of networking and troubleshooting. The user should check the possible causes of the issue and try to eliminate each cause until the correct one is identified.

In this scenario, the user is unable to communicate with a host on a different department of the company but has no issue communicating with others on the same subnet. Other hosts on the subnet can also reach remote hosts. Based on this information, we can eliminate options A and B as incorrect subnet masks would affect all communication outside the subnet, not just one specific host.

Option D can also be eliminated as the WINS server is not used for basic network communication, and the issue is only with one specific host.

Therefore, the correct answer is:

C. Incorrect default gateway on your computer

This option is the most likely cause of the issue as the default gateway is responsible for forwarding traffic to remote networks. If the default gateway is not configured correctly, the traffic will not be directed to the correct destination, resulting in the inability to communicate with remote hosts.