Is my network card faulty?

You may need to consider the possibilty that you are infected with malware and it has corrupted your TCP/IP stack. Or in general your TCP/IP stack could be corrupted. Here are some links and specific references from those links.

Reinstall and Reset TCP/IP (Internet Protocol)

1. Click on Start button.
2. Type Cmd in the Start Search text box.
3. Press Ctrl-Shift-Enter keyboard shortcut to run Command Prompt as Administrator. Allow elevation request.
4. Type netsh int ip reset in the Command Prompt shell, and then press the Enter key.
5. Restart the computer.

note: if you're using manually assigned TCP/IP settings, take notes as this will reset to the default 'automatically obtained'

Fix Winsock Manually on Windows 7

1. Open up the command line utility and enter:

   netsh winsock reset catalog (resets winsock entries)
   netsh int ip reset reset.log hit (resets TCP/IP stack)
   

2. Reboot your PC

References

http://windows7themes.net/winsock-fix-for-windows-7.html
How do I reinstall the TCP/IP protocol driver on Windows 7?

I would suspect the NIC. Replacement NICs are cheap, I'd not hesitate long before buying one.

Other ideas...

• Move the patch cable to a different port in the hub, switch or router.
• Replace the patch cable
• Boot a different O/S (e.g. Linux Live CD)
• Check fans, internal temperatures.

Microsoft's Knowledge-base has a long list of diagnostic suggestions.