Unable To Login At Start Up

Strange issue today
During boot up of laptop power cable came out and machine turned off before login completed.
Started all up again and now I can not get past the log in screen as it says my passowrd is incorrect.
Even more strangely the password hint didplayed has nothing at all to do with the password I have been using for some years on the machine.
Have tried restart/shift key option but still if I want to go further my password is denied.
Im now stuck looking at log in page.
Even booting up with F2 i am again asked for password.
Could the machine have been hacked ? virus?
Anyway around this ? or will I have to rip hard drive off in order get at my files
Acer Aspire A717-71G
Windows 10 64 bit

 

Deffo scrambled files. The battery was left out and in another room after cleaning etc. I used to log in with a 4 digit pin. Now asks for password and none i have matching the hint work at all. There is now no option to change between pin pass and finger print as before.
I have a few weeks worth of docs and photos on the drive which have not been backed up and I would like
to geet at them before I go down the reset route and loose all user files. The USB media I have which has what I thought recovery data on are not being recognised either.
Any workaround for this
TIA

 

Step 1. = Right-click on the Windows start button on the bottom left-hand corner of the screen to open the settings menu.

I have no windows start button
All I have is the sign in page asking for a password. I used a pin. there is no options to change to a pin

 

Cheers guys
UPDATE -
I did manage to get the OS back up and running following your advice and links, however, I never had (or seen) any options of what to save, but most of my stuff was there apart from a few months of photographs in folders taken this year. Strangely It did recover lots of word and pdf docs from this year.
Ive looked in "windows old" and the missing stuff aint there, but hey ho, lesson learned and at least I have a laptop which is now useable again.
Thanks to you guys for the assistance.