Hi guys , just an update i did replace the wallet from one from 2015 and it did not work with the old password  .
 So after getting all worked up i tried the password again the new encrptyed one and it worked, so to be honest i was scratching my head for a bit , so after i copied and pasted the new password i have now made a back up of the wallet and my password, so all good. Ohh and for the record an old wallet with the old password doesn't work. so you can't fall back to that if you make a new password, thanks again for all who took the time out to help me, hope you all stay safe.
Thanks.

Yes i have the old install on the external HD, also the walet.dat file is in there, i have a copy of the old wallet.dat file on 3 USB pens as well all encrypted. also the password before i changed it for it.. NotTethered I cannot guarantee that i didn't copy anything else along with that password, i know what your saying but i can't see it, but also not 100% on that . Ewaspiro i havn't got a clue where you got or think i bought a fake wallet as i can assure you it is not. I mined on this site for years. I just wanted to ask some questions before i make a move incase i make the situation worse, if it can get any worse, if i sync the old dat file back, would i be able to open it with the old password.

Sorry i meant copy the dat file across like you say, was just wondering if i would be able to decrypt that wallet using the old password. i have only ever changed it once, and that was last week and now it does't work, like i said am 100% sure it's the right password. I will try in a bit , thanks just now.

Hi everyone, I've been having a few problems with bitcoin core so i will start at the beginning and hope i can get help here, thanks.
It started a few weeks back, i ran bitcoin core through windows on to an external drive. the drive was playing up and taken ages so upgraded the pc and download direct to C drive . I had, have most things backed up including a few wallet.dat files. After i download the newest version of bitcore and synced the blocks i copied over the wallet.dat but the wallet would not sync. If i remembered right i went to the command line and asked it to sync the wallet and it did, A few weeks later i tried to open the wallet by clicking file Open wallet and an error message popped up (Berkelybatch Can't open database wallet.dat( dupllicates fileid ef95020000001700099f6ad130000000000000000 from wallet.dat) So after that i opened on bitcore settings change passphrase, i entered my old password, and replaced it with a new one i copied and pasted, restarted bitcoin core and now it will not accept my password, i am 100% sure it is the correct password, I have the old wall.dat files from 5yrs ago and the new ones backed up, i was looking for any input before i try to do anything,  can i upload the old wallet .dat file and enter the old passphrase or is that a no no? any help appreciated and thanks in advance for taking the time to read it.