password not working

Yesterday I decided to upgrade the hard drive in my iMac G5. So I put in a 500 GB drive and reinstalled leopard. Everything worked great. I got to the part to migrated data from time machine which I did. It took about 12 hours to get everything back. Now this morning I boot it up and it gives me the registration info again. So I fill it out then it gives me the login screen with my two accounts. I go to login and it just shakes like the password I entered was invalid. After a few tries it gives me the "hint" but I am POSITIVE it is the correct password since it's the one I have been using for the last 3 1/2 years on the machine. I tried using a different keyboard just to make sure it was typing it in correctly but it still doesn't work. At this point I don't know what to do. Is there any way to reset the password? Any suggestions on why this is not working?

You can do that by booting up from your Leopard install disk
Mac OS X: Changing or resetting an account password

Scroll down to where is says

Resetting the original administrator account password

Wait a second, I thought that if you reset your password then the info/files on the account got wiped;

please anyone, if I am wrong, say something!!!

I just had this with the Macbook and had to reinstall from the disc to get access to the machine. I'm sure the passwords were good, but something weird sent it nipples up.
If it starts that shaking game again it may just go into orbit.

Same for me...I upgraded? to SL and have had printer issues and Word 2008 crashes. So today I re-boot and it flips me over to the guest account. So I figure, no problem, I'll just go back to my user account. I typed in the password and got the shaker display...oh oh! So it won't recognize my password? I tried re-setting it using the old Leopard disk, but it won't take. Inserting the SL disk only allows me to re-install Snow Leopard. What to do now? Do I need to do a clean install back to Leopard?

Slabman, I had to do a clean install from the Leopard disk. Put the coffee on and think positive thoughts; we could be malletting a Windows PC instead of waiting calmly for the Apple to come back to us.

That's what I was afraid of. I want to revert back to 10.5, but not sure of all the details in doing a clean install. Will my TM backups give me all the files I need to get back to the old setup? I assume I will have to re-install all the apps, however......

Still think ol' Bill Gates had a hand in this Opsys.

The reinstall went very smoothly, and gave us an "opportunity" to reselect the applications we actually need on the Macbook. (Don't you just hate 'management' speak) The TM should have everything retained.

Bon chance, courage mon brave!