Startup password

Hello,

I just purchased a d260 mini secondhand and I stupidly thought I could change the administrator name, but of course it would not let me change the password since I did not have the original password. I could log on previouisly without it, but since I changed the admin name, when I shut it down, it now wants the old password with the new admin name. I am by no means computer literate, so this came as quite a surprise. I did not realize that changing the admin name would cause this problem, since I could logon without a password before. So now I can do nothing since the startup login requests the password. any suggestions that I can handle myself. many thanks