Windows XP logon and lock password problem


Yesterday I changed my password for user account I'm using in Windows
XP SP2. I am also an administrator and only user of this PC. It is
business policy of the company I am working for that PC must be locked
when user is not present (also password protected screensaver must be
active after 10 minutes of idle - in case I dont manually lock my

Problem is next: When I boot up my machine, logon screen is shown, and
I can normally logon with newly changed password. After that, if I try
to lock my computer, or screensaver becomes active, I am prompted for
my password, and when I type it, it says it is incorrect and that I
should try again. I am 100% sure that password is correct since I can
normally logon if I restart my machine or choose logoff and then again
logon with this password.

I have very slow machine and this is very irritating for me, also we do
not have local admin who can solve the problem quickly, rather we have
some strange globalized helpdesk which are not helpfull and quick in
solving this types of problems.

I tried patching my Windows on Microsoft update, and also (and this is
quite strange) when I go in Users in Control panel, and try to change
the password, it again says that I am not entering the right current
password. Once again, THIS IS 100% correct password since I can
normally logon when Windows starts.

So help is needed please :)