Somehow (I really don't know how/why, and no I didn't forget it) Ubuntu doesn't accept my root password. On my hard drive I have 4 partitions, two with Windows 7, two with Ubuntu 11.10.
I want to re-install Ubuntu on the same existent Ubuntu partitions.
So - if I first delete these two partitions and then re-install Ubuntu does it mess up my Grub booting process?
What is the simplest and safest way to re-install Ubuntu without messing up my Windows OS? (Please remember that I can't access any of Ubuntu's administrative functions since it doesn't accept my password.)

Before you go about reinstalling, did you SET a root password? By default, root account is DISABLED in Ubuntu. You are not trying to use sudo and trying a different password right? If your user has administrative privileges, you should use your account's password.

To answer your question about reinstalling, I have installed ubuntu over an existing installation as if I am installing it for the first time. The GRUB generated by the older installation was overwritten by the newer installation (for me). And yes, I am talking about dual boot installation.

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nonamedotc, thank you very much for your reply. Very helpful, and re-assuring