I used to run LW 4.12.4 properly before. but somehow a few days ago when I try to run it, I was double click on the LW sign and the LW box was pop up state that LW is loading after that there was notthing happen. I was try to reinstall it but the same problem happened again. I have no idea how to fix it. help me pls, thanks.

Remove your old version of Java & reinstall JRE using the offline installer here
http://java.sun.com/javase/downloads/index.jsp

If that doesn't help, try deleting the preferences folder when LW's properly closed (points 2 & 3 below)
Fixes for LimeWire

If you want to reinstall LW, use the offline installer
http://www.limewire.com/english/content/download.shtml