I hope someone can help start up probs with mini mac

Hello. I am at my witts end lol. I have a mini mac that was given to me new about two years ago. about six months ago my monitor went off and would not come back on. So for about two months I didn't mess with it and then one day I tried the monitor and it came back on. so I turned on my mini mac and when it booted up I got the screen that it was loading then all of a sudden it had my name tonnie computer then under that it has screen name and password. I have never gotten this screen before and can't get around it. i didn't have it where i had to insert a screen name or password. I do not have the disk that i have read about so could someone please tell me if there is a way to get around this? I did hit the option button at start up and it came up with a button on the left hand side that looked like a refresh button, the middle button was a picture of a computer, and to the right was a button that had a right arrow. and there was a time clock running but then it went right back to the screen name and passord needed ..........any help is greatly appreciated. Thank you,
Tonnie

G'day and welcome to the Forums.

Looks like you are going to need the install DVD to enter a new password. Is it running TYiger OS X.4 or Leopard OS X.5?

i belive it is tiger. i am not real proficient with macs.