I add downloaded messenger to my emachines ET1641-02w

What is the Messenger that you downloaded? If it's third-party not even from Microsoft or Yahoo then you will encounter problems. So what you can do is run a Windows Recovery instead and see if it will boot normally. If it doesn't then what you can do is turn it off completely wait 30 seconds for it to cool down and then turn it back on. See if it passes the Windows Welcome Screen and allows you to boot right into the system.

1. Turn off the system completely. Wait 30 seconds and turn it back on.
2. Press F8 and then from the menu select: "Last known good configuration from the menu", then all you do is let it use then it should boot normally.

3. If you have the CD to Windows XP Home/Pro then insert it but don't press anything until it boots into Windows normally.

Note: It could just be that while it was installing the software it was rewriting the registry and a failure occurred while it was writing. Sometimes third-party software is suspected to make changes to the OS so it would change things at the sametime.

4. Keep the CD in there don't take it out until it allows full activation of Windows to show in front of your screen.

I hope these steps work out for you and please keep me updated as well.

Registry looks to be corrupted.

As you boot the computer, press F8. You'll get the boot menu. Select 'Safe Mode with Networking'. Now the computer should be able to get into Safe Mode.

Get on to internet, Start a free registry scan from www.registryfix.com

If this fails, you may need the Windows Installation Disk to fix it.

E machines have problems like this. unplug it from the back of the computer for ten seconds, plug it back in, do a start mode> If this does not work try rebooting to an earlier time