原来从网上下载.chm 文件，发现只能打开目录，然后我就删掉了，今天在网上看到了一个解决方法
If you downloaded the file with Internet Explorer, it probably looks like this:
Internet Explorer marks the file as "potentially dangerous" since it came from another computer. When you try to view a .CHM file that is marked like this, Internet Explorer refuses to show the content (a .CHM file is nothing more than a bunch of packaged-together HTML files).
To fix this problem, find the .CHM file on your hard disk. Right click it, and choose Properties. You should see a window that looks like this:
Click the "Unblock" button, then click the "OK" button. Now you should be able to view the .CHM file properly.
I hope it's helpful.