You can try:
Forgot Your Account Password
For Lion/Mountain Lion
Boot to the Recovery HD:
Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
When the menubar appears select Terminal from the Utilities menu.
Enter resetpassword at the prompt and press RETURN. Follow
instructions in the dialog window that will appear.
Or see Reset a Mac OS X 10.7 Lion Password, OS X Mountain Lion- Reset a login password, and
OS X Lion- Apple ID can be used to reset your user account password.
For Snow Leopard and earlier with installer DVD
Mac OS X 10.6- If you forget your administrator password
For Snow Leopard and earlier without installer DVD
How to reset your Mac OS X password without an installer disc | MacYourself
Then fix the 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:
1. Open Keychain Access (located in Applications/Utilities)
2. Go to the "Keychain Access" menu and select "Preferences"
3. Click the "First Aid" tab
4. Make sure the "Synchronize login keychain password" box is checked
5. Close the Preferences window
6. Go to the "Keychain Access" menu and select "Keychain First Aid"
7. Enter your username and password
8. Click the "Repair" button
And, if this all fails to help then:
Reinstalling Lion/Mountain Lion Without Erasing the Drive
Boot to the Recovery HD: Restart the computer and after the chime press and hold down the COMMAND and R keys until the menu screen appears. Alternatively, restart the computer and after the chime press and hold down the OPTION key until the boot manager screen appears. Select the Recovery HD and click on the downward pointing arrow button.
Repair the Hard Drive and Permissions: Upon startup select Disk Utility from the main menu. Repair the Hard Drive and Permissions as follows.
When the recovery menu appears select Disk Utility. After DU loads select your hard drive entry (mfgr.'s ID and drive size) from the the left side list. In the DU status area you will see an entry for the S.M.A.R.T. status of the hard drive. If it does not say "Verified" then the hard drive is failing or failed. (SMART status is not reported on external Firewire or USB drives.) If the drive is "Verified" then select your OS X volume from the list on the left (sub-entry below the drive entry,) click on the First Aid tab, then click on the Repair Disk button. If DU reports any errors that have been fixed, then re-run Repair Disk until no errors are reported. If no errors are reported click on the Repair Permissions button. Wait until the operation completes, then quit DU and return to the main menu.
Reinstall Lion/Mountain Lion: Select Reinstall Lion/Mountain Lion and click on the Continue button.
Note: You will need an active Internet connection. I suggest using Ethernet if possible because it is three times faster than wireless.
