I changed user account and now Time Machine won't back up.

A few months ago I had a problem with my user account. I can't remember the details but i think it would no longer accept my password. After doing some hunting around for answers i made a new user account with administrative priviledges and transferred all the files over to that account. I also changed the permissions on those files to allow me to access them as a new user identity. For the most part that seems to have worked for me, although possibly i have not done the right thing.

Anyway, i have just realised recently that although the little circular arrow that indicated that Time machine is backing up my files, it hasn't actually made a backup since the end of august, which was possibly when i did this funny thing with my user account.

I am assuming that Time Machine has just got very confused about the disappearance of my files from the previous user account and change of permissions etc.

What can i do? I read on 'pondini.org' that i could reset my time machine by deleting the preferences file from my system library and then rehooking up my external hard drive as the desired backup volume. It would then, i assume make a full backup to begin with?

Any advice gratefully received. I am a graphic designer and i do need to have my files backed up!

thanks

Lesley

ps i had some extra RAM installed a little while before the user account problem and only mentioning it here in case that is an issue with Time Machine as well.