You've not told us
which password you're referring to, Henry.
It could be a BIOS password. In which case your screen might look something like this:
http://www.passwordunlocker.com/images/knowledge/bios-password-01.jpg
Or, probably more likely, it's the Windows password. In which case, your screen might look like this:
http://www.bleepstatic.com/tutorials/windows/lock-your-screen/windows-7-locked.jpg
Or, again, it could be the password to a specific service, such as your email.
In the absence of further information, I'll assume that it's the Windows password which you're referring to:
Firstly, make sure you know the name of your account. It's what appears above the password field. (In my second link, above, the account name is 'User').
Then try following the instructions under "1. Bypass Windows 7 Logon Password with Command Prompt", here:
http://www.isunshare.com/windows-7-password/bypass-windows-7-logon-screen-and-admin-password.html
(NB: Replace 'iSunshare', in those instructions, with your own account name. Replace '12345' with whatever password you want to use).