A couple of common causes.
1] Explorer, (which includes your Desktop, Documents folders, Windows Explorer), is attempting to render either a video thumbnail or an image thumbnail which is corrupted.
If this happens directly at startup, there may be a corrupted video or image file, (the actual file, not a shortcut icon), on your Desktop. If it happens when trying to use Windows Explorer to manage files, make sure the files are listed in Details or List option, and not thumbnails or icons option. WE doesn't try to render files in either Details or List options.
2] A bad or corrupted IE Add-on. Internet Explorer is now closely integrated into Explorer and what affects one can affect the other. Look at IE's Add-ons, (IE > Tools > Manage Add-ons), and star elimination testing. A quicker way is to Reset IE, (Tools > Internet Options > Advanced tab, then Reset), but you may lose all favorites, history, cookies, and web site logins if you use that.
Yesterday my computer started doing this, and it's pretty annoying. The message windows explorer has stopped working appears. Windows searches for a solution, then windows explorer restarts. Also, when I go to the start menu and click on computer it takes way longer for the icons and everything to load than it used to. Going to my computer is a sure way to get the error to appear as well. I have restarted in safe mode and the problem happens there as well. I have also ran a couple different virus/spyware scans and am fairly sure the computer is clean. Any ideas on how to fix this? I would like to avoid reinstalling windows and starting from scratch. Thanks!