How can i delete a administrators account without the password?
I bought laptop from ebay I am the 3rd owner; 2nd owner had no password got password changed but still wont let me in as admin.
I need to delete the first owner's admin account to get a second-hand laptop to work; I can't reinstall Ubuntu because I can't play DVDs.
I can only login to the guest account.
You can reset password of any account by booting into the Recovery Console and using passwd command there:
passwd john
after which you should be able to log in.
Alternatively, you can boot from an Ubuntu LiveUSB and use chroot command to access to passwd command on the laptop's hard drive as root.
HOWEVER, if you bought the laptop on ebay, I would strongly advice you to perform a full re-install of the system - using it as-is is just not safe, nobody knows what the original owner installed there.
To perform a fresh install you don't need admin permissions on the laptop - you simply put a CD in the tray or plug in a USB flash drive and reboot the system. You may need to go into laptop's BIOS settings and make sure CD drive or USB comes before the hard drive in the list of boot devices.
Sorry, without administrator (root) access you can't do much.
Please try reinstalling Ubuntu from a USB...
You can try to reset the password for the Administrator account ...See this answer on how to do that
After reseting the password you can create a new administrative account for yourself and delete the old account.
To create a new account open the User Accounts program form the dash, unlock the program by clicking the unlock button on the top right of the box---use the password you created during the previous step. Then on the far left click the + sign to create the new account and make sure you create it as an Administrator. You can then use the - sign to delete the old account(make sure it is highlighted)
I have included a screenshot below but it is from 12.04 so it might be slightly different but it should be close enough to help.
