Can you give us a little more information:
1. What browser are you using? (Try on a different browser eg: IE, Firefox, Chrome etc...)
1.1 Read about netflix problems on Microsoft:
Known issues and limitations for Netflix on Windows Media Center for Windows Vista
2. Can you do a system restore to the time it was working?
3. Have you installed any drivers and\or updates between the time it was working and now? Did you use any registry cleaners? If so, undo the changes.
4. Download and install the latest versions of your audio, video and network adapter drivers. Video display or audio glitches can occur if you have outdated or incorrectly functioning hardware device drivers.
5. Are you getting some "e r r o r - code"? If so, what is it? Also, what was the whole message from the Netflix help?
6. Are you using wireless connection? If so, that might be the problem. If not, you may need to ask your ISP how to open ports.
7. Some have reported virus the cause of this. Run a scan and make sure your AV is updated and working properly.
These are just starters...