RESOLUTION
In order to retrive your plesk admin password, you will need to follow these instructions:
1) Log into your dedicated server as an administrator
2) Click on Start > Run. Type CMD.exe and press Enter. A black DOS window will apear.
3) Type cd %plesk_bin% and press enter.
4) Type plesksrvclient.exe -get and press enter. Your plesk admin password will be displayed.