Which program did you install recently, specially a program that installed right-click context menu items ?
If you do not know here is an example : all Anti-virus software install right-click context item for scanning a selected folder or file.
Problem with some such context menu handlers is that they are programmed badly or are incompatible with current version of Windows and hang up the system. You can download FileMenuTools from http://www.lopesoft.com/en/
to enable disable them.
Experiment by disabling the items one by one and see if it makes any difference.
Edited by Romeo29, 27 March 2010 - 04:47 PM.