It sounds like you have installed a package via an installer. The windows one for sure does not have all the dlls available. What you can do is download the ZIP version of php (not the MSI installer) and take the dlls from the zip package and move them into the EXT folder...
I did exactly what you said:
I added the following 2 lines of code in the Dynamic Extensions area of the file C:\Program Files\PHP\php.ini
I downloaded the ZIP version of php-5.2.8-Win32 , copied and pasted the two files ( php_mbstring.dll and php_mcrypt.dll ) into the folder C:\Program Files\PHP\ext
Then finally I restarted the web server Apache.
When I open phpMyAdmin in a browser, the 2.error (The mbstring PHP extension - Error) is eliminated, but the 1. error ( Cannot load mcrypt extension. Please check your PHP configuration.)
is still there !
What the reason can it be ?
Kindly Amanda Nguyen