Q: I cannot proceed to install EL Capitan after downloaded because my Apple ID not accepted although keying correct password

Okay, so you haven't gotten very far into the installation.

Here is how to reset a forgotten password.

Do you have a backup made prior to the upgrade, such as a Time Machine backup?   (Keychain is not where the administrative password is stored, unfortunately.   Deleting the login keychain causes all of the remembered passwords in Safari and elsewhere to be lost.)   If you have that, I'd recover the login keychain from there.

If you do not have a current backup, that's the first think you'll want to get.

There might be a problem with the disk structure or protections, or with the disk itself.    Creating a new keychain should not be blocked, short of a permissions error or a disk problem.    Disk Utility and verify the disk, and see if there's something going on.   (Unfortunately, some of these steps can require an administrative password.)   You can try the repairs or a disk backup by booting from the recovery partition — that won't require administrative privileges — and try a repair or recovery from there, or back up the entire disk to an external scratch disk.

Do you have another Mac around, where some tools can be built and then might be used here?

Allow the service to use the keychain.

The pop-up that you are reporting usually has some buttons that will tell OS X that you wish to deny access, to allow access once, or to always allow access, for the specified application or service.    Deny denies the access, and the app might ask again later, depending on what you're doing.   Allow once causes the application to be granted access to look up your passwords and other data in the keychain.  Always allow grants the application permission to access your passwords when needed and until that permission is revoked.

The login keychain is either corrupted, or the specified password is incorrect.

There is no means to recover the contents of the keychain without the password — the contents are encrypted.

Do you have Time Machine configured?   If so, use Finder to go to the folder with your keychains, and enter Time Machine, and restore the file that was deleted.   This should get you back to the initial state, when you were lacking an administrative password.   Post a reply after you have restored the keychain from the pre-deletion Time Machine backup.

If you don't have a Time Machine or some other system backup here, then please go get Time Machine or some other backup software configured and started — right now.   Then you're going to want to either remember what the password to the current keychain was, or rename the keychain file and create a new keychain.