I had the exactly the same senario as you,knew I was using the right password but it wouldnt let me in,googled it but even for somebody who knows their way round a pc,it seemed to be fraught with possible errors.What I did was use the restore partition to reformat the hard disk,it would depend on the laptop having a recovery partition if you could use this method.What make and model is it.
I have inherited a laptop running Windows XP from a relative who has given me their password to get past the first screen. They havn't used the laptop for a good few months now.
When I get the password prompt I enter the given password (all lower case-yes I checked). The machine doesn't reject it immediately but goes onto a screen saying 'welcome' whilst the centre bit spins .After about 30 seconds it goes back to the log in screen saying incorrect password. Relative is adamant I have the correct password.
Any ideas about how I can circumvent this bit and remove the password? Thanks in advance