Yesterday, my computer (running XP Home edition) all of a sudden switched themes and I can't find a way to switch it back.

Before, my login used to look like this:
http://www.guidebookgallery.org/pic...

But now it looks like this:
http://vcl.ncsu.edu/eweImages/help/...

Also, pressing ctrl-alt-del no longer brings up the task manager, but instead brings up a login screen.

I spent an hour and a half searching on Google to fix this problem but I couldn't find anything at all! If anyone knows how to fix this please help me!

Open Control Panel, User Accounts.
Click "Change the way users log on or off".
Is "Use the Welcome Screen" checked?

And on the left, click on "Logon Options" for details.

There are other ways of setting this up, I just can't locate it at this moment. (It's ~somewhere~ in my (self constructed) "Computer Info" partition.)

It's a good day when you learn something

Thanks! That lead me to the error message I needed.

Turns out that after installing my wireless card, it for some reason installed RtlGina.DLL as a login file which prevented the regular startup.

I went to the Netgear website and found the registry to delete. And now it works again!

You're welcome. Glad it helped.

It's a good day when you learn something