Ohhhk,
Since you are using Windows 7, please try following method:
Open up windows explorer and then paste the following text into the address bar, which should bring you to a folder with a single folder inside with a really long name.
%userprofile%\AppData\Roaming\Microsoft\Protect
What you’ll need to do is just rename that folder to something else then re-open Outlook and type in your password.
If it not works, you can try to add this registry entry.
1. Click Start, click Run, type regedit, and then click OK.
2. Locate and then right-click the following registry subkey:
HKEY_CURRENT_USER\Software\Policies\Microsoft\Office\14.0\Outlook\Security
3. Point to New, and then click DWORD Value.
4. Type PromptForCredentials as the name of the new registry entry, and then press ENTER.
5. Double-click the PromptForCredentials registry entry, and then type one of the following values in the Value data dialog box:
00000000
Note In this case, cached credentials will be used.
00000001
Note In this case, users cannot use cached credentials. Users are always prompt to provide a user name and password.
6. Click OK.
In addition, you can try suggestions provided here:
http://support.microsoft.com/kb/956531