To determine the exact error code you’re getting in Windows Live Messenger, click the “Show details” option from the dialog box that pops-up when the sign-in attempt to the service fails. Take note of the error and specify it when you contact support through http://support.live.com

This image illustrates how to get the error code from the pop-up you receive for a failed sign in attempt to Windows Live Messenger.

Sign-in issues with Windows Live Messenger can be triggered by a wide array of probable causes. It might be due to as simple as an incorrect date and time settings on your computer, or as complicated as problems with your Internet connection.

We've listed some troubleshooting steps below that may help resolve the problem. Follow the steps appropriate for your computer's Windows Operating System.

1. Check Date and Time Settings

WINDOWS XP

a.  Click Start, click Run, type control timedate.cpl , and then click OK. 
b.  In the Date and Time Properties dialog box, confirm that the date and time settings on the computer are correct, and then click OK. 

WINDOWS VISTA

a.  Click Start, type control timedate.cpl in the Start Search box, and then press ENTER. 
b.  In the Date and Time Properties dialog box, confirm that the date and time settings on the computer are correct, and then click OK. 

2. Configure your Firewall Settings

To configure Windows Live Messenger through the most common firewalls, visit:
http://messenger-support.spaces.live.com

Refer to "How to enable Windows Live Messenger through your firewall" under the FAQ section, click the link for the firewall that is installed on your computer, and then follow the steps on the screen.

However, if you have a firewall that is not listed, see the firewall manufacturer's documentation or contact your firewall manufacturer to configure Windows Live Messenger.

3. Upgrade your Windows Live Messenger to the latest version. Get if from http://download.live.com

4. Clear the Check for Server certificate revocation (requires restart) check box.

a.  Start Internet Explorer. 
b.  On the Tools menu, click Internet Options. 
c.  Click the Advanced tab. 
d.  Under Security, uncheck the Check for Server certificate revocation (requires restart) check box. 
e.  Click OK. 
f.  Exit Internet Explorer. 

5. Delete the Windows Live Contacts folder and Messenger cache. This will make sure that the locally stored information related to your account is refreshed on Windows Live Messenger.  

Change the Microsoft Windows Explorer settings. To do this, use one of the following methods:

WINDOWS XP

a. With your mouse, right-click the Start button, and then click Explore to open Windows Explorer. 
b. On the Tools menu, click Folder Options. 
c. On the View tab, in the Advanced settings list, select Show hidden files and folders under Hidden Files and Folders. 
d. Clear the Hide extensions for known file types check box. 
e. Click OK to close the Folder Options window. 

WINDOWS VISTA 

a. With your mouse, right-click the Start  button, and then click Explore to open Windows Explorer. 
b. On the Organize menu, click Folder and Search Options. 
c. On the View tab, in the Advanced settings list, select the Show hidden files and folders check box under Hidden Files and Folders. 
d. Clear the Hide extensions for known file types check box. 
e. Click OK to close the Folder Options window. 

Delete the Windows Live Contacts folder. To do this, follow these steps:

Note: Before doing these steps, make sure to exit Windows Live Messenger and that it is not running on the background. To double-check this, open the Task Manager window and check whether the msnmsgr.exe is running on Processes.  If it is, select the application and click End Process. If you are prompted, click Yes.

To open the Task Manager:

WINDOWS XP: Click Start and then Run. Type taskmgr.exe and click OK.
WINDOWS VISTA: Click Start and then type taskmgr.exe on the Start Search box. Press Enter on your keyboard.

a. Right-click Start, and then click Explore to open the Windows Explorer window. 
b. In the Windows Explorer window, locate the folder for the operating system that you are using: 

WINDOWS XP: C:\Documents and Settings\ Your Windows logon name \Local Settings\Application Data\Microsoft
WINDOWS VISTA: C:\Users\ Your Windows logon name \AppData\Local\Microsoft

Note: In these examples, Windows Logon name is the logon name that you use to sign in to Windows.

c. Delete the Windows Live Contacts folder.

Re-launch Windows Live Messenger and try to sign in again, and verify if the issue remains.