The probable cause of a computer being able to access devices on the same network but unable to access devices on other networks is most likely an incorrect or missing default gateway configuration. The default gateway is essential for routing traffic outside the local network. If the computer's default gateway address is invalid or missing, it will only communicate within its local network and fail to reach devices on other networks. Other potential causes could include:

• Incorrect IP address or subnet mask settings
• Firewall settings blocking external network access
• Router configuration issues

However, since the computer can access devices on the same network, the primary issue is usually the default gateway configuration being incorrect or absent.