Python not starting

[rama29065 at gmail.com]

I was using python from over an year and half.Suddenly from yesterday i'm unable to run it.
The error is as follows
Traceback (most recent call last):
  File "C:\Python27\lib\site.py", line 563, in <module>
    main()
  File "C:\Python27\lib\site.py", line 546, in main
    known_paths = addsitepackages(known_paths)
  File "C:\Python27\lib\site.py", line 324, in addsitepackages
    if os.path.isdir(sitedir):
  File "C:\Python27\lib\genericpath.py", line 44, in isdir
    return stat.S_ISDIR(st.st_mode)
AttributeError: 'module' object has no attribute 'S_ISDIR'