Mac keeps on asking for password to delete files
You "changed" the root username?

Can you elaborate on the process you use? I suspect you created a new account and then copy and pasted the files from the previous directory, roots home directory, to your new user. If this is the case you will likely need to use Terminal (Applications/Utilities/Terminal) to restore the permissions on them as root is probably still the owner. Assuming your username is bob execute the following commands in terminal.

Change the owner of the files to your user:
sudo chown -R username:staff /Users/bob

Change the permissions of your home drive to 600. (Owner read/write, everybody else denied):sudo chmod -R 600 /Users/bob

Let us know how you go or if you need more detailed instruction.

If you have a copy of the OSX DVD I believe there is a utility on it to repair home drive permissions but I can't remember it offhand, sorry.