You should have set a password hint when you first created your password. To see it, enter any old rubbish into the password field and hit 'Enter' (or click the arrow button). You'll then see an error message, telling you that the password was incorrect. Click 'OK'.
You'll then be taken back to the password screen but your password hint will be underneath the password field itself. I've just tried it on one of my old Windows 7 netbook. My hint reads "Son and his boys in age order (with capitals)", which would be enough to remind me what my password is but which would be meaningless to anyone who stole my netbook. Your hint will show whatever you wrote when you created your password. (e.g. "Mum's maiden name", "My first pet's name" or "My place of birth). That will hopefully help you remember your password.
If you can't get in via your password hint (and Tuvok's administrator route won't work for you), the only way that I know to get in is to check that the BIOS is configured to boot from a USB memory stick, then insert a memory stick which has specialist Linux software on it for hacking Windows passwords and boot the device from there. I'm not even going to attempt to provide you with detailed instructions for that method though, Henry, as I feel that it would be far too technical for you to understand. (I've used that method myself a few times, to unlock password-protected computers that I've bought at auction but it took me quite a while to work out how to do it. It's definitely a job for specialists, as the whole point of passwords is that they're meant to be difficult to hack).
So, regrettably, if you can't remember your password (perhaps with the help of the password hint that you created) or get in using Tuvok's link, you'll have to take the machine to a computer repair shop. They should have a password-hacking USB stick, enabling them to find your password in just a few seconds.
In future though, I suggest keeping all of your passwords written down somewhere (where you won't forget where the list is). I've got several hundred passwords, all of which are recorded in a folder on a shelf above my desk. If I ever forget a password, I know that I'll be able to find it in that folder.