Windows 10 password won't work suddenly

Same password for years stopped working after I'd tried getting into safe mode ( never actually got to safe mode) I rebooted a few times and then the problem came about. Its a pin number I use which registers as soon as last number is typed. Now it is sane screen but I can type as many digits as I like but I will have to press enter at end to check if correct. I have a feeling it has reverted to an old password as it gives a clue. I cant do system restore or anything as I need to enter that same password. I assumed I was on admin profile because its the only profile. The reason I was trying to get to safe mode was to delete a bitdefender file that wouldnt budge as I was prompted that it was open elsewhere. It wasnt as far as I know. Im the only person who uses laptop. I have never posted on this kind of forum before. I usually get to bottom of problems but not this one. HELP

See these links:

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Linux to the rescue! How Ubuntu can help a computer in distress | PCWorld

Is it a Local account PIN or a Microsoft account password it is asking for? If the Local account PIN doesn't work then try your MS account pasword if you have one.

A PIN is not a Password; they are not interchangeable. Windows 10 tells you which it expects in the input box:

I have a DELL laptop and a HP desktop and both are Local account machines. Both ask for a "Password" and we enter our PWs but these are not our MS Account PWs. I was wondering if the OP had inadvertently switched to MS Account mode during his/her attemts at safe mode.

My comment that a PIN is not a password was for @Zipped, but I don't think you can switch inadvertently​ between local and Microsoft accounts.