User access Password rejected on first keypress

Trying to logon, I get "incorrect password" the moment I press a key.
Every time except one, I then get the chance to put in the correct password.
One time the screen dropped the logon box and hung there doing nothing.
I used Ctrl/Alt/Del to make it return to the logon screen.
I have scanned for virus and spyware.

I have had lots of trouble with this ***** computer. Freezing desktop is
the usual thing, but there is a link.
When I use CtrlAltDel on the frozen desktop, sometimes I get an error that
the
computer has failed to create a security dialog, or something similar.

Any help would be wonderful.