I'd start with the following steps, you have a couple of options. Keychain app is in Applications/Utilities. Think of a keychain as a real keychain but on your computer each key unlocks a resource like a web page with a username and password. Web page passwords are part of the login keychain.
First, if you've forgotten your password, you can use the "Keychain First Aid" utility to make the keychain password the same as the login password.
This can be accomplished via the following process:
Open Keychain Access (located in Applications/Utilities
Go to the "Keychain Access" menu and select "Preferences"
Click the "First Aid" tab
Make sure the "Synchronize login keychain password" box is checked
Close the Preferences window
Go to the "Keychain Access" menu and select "Keychain First Aid"
Enter your username and password
Click the "Repair" button
Another option is to completely delete your keychain then recreate it. This routine is useful if your keychain appears to be corrupt or otherwise inaccessible. If you do delete it you will need to re-enter your user names and passwords the first time you return to web pages that require it. After the first time entering values, future requests should consult your login keychain when using Safari.
This can be accomplished as follows:
Launch Keychain Access (located in Applications/Utilities)
Click "Show Keychains" in the lower-left corner of the window.
Select the problematic keychain from the left-hand pane.
Navigate to the "File" menu and select "Delete Keychain '(name of keychain)'"
Check all options for deletion and press "OK"
Create a new keychain by going to the "File" menu, then "New" and selecting "New Keychain"
You can now make this keychain your default if you desire by selecting it, then going to the "File" menu and selecting "Make '(name of keychain)' Default"
