PROBLEM WITH WINDOWS XP WINLOGON SERVICE

I HAVE A PC WITH WINDOWS XP INSTALLED.
RIGHT NOW I HAVE A PROBLEM,THE PROBLEM IS THAT WHEN I LOGON TO MY SYSTEM THE (WINLOGON) SERVICE IS TAKING 100% OF CPU USAGE, WHEN I OPEN ANYONE APPLICATION THE SYSTEM IS GOES IN HANG CONDITIATION.PLEASE HELP ME TO SOLVE THIS PROBLEM.