[SOLVED] log in as user problem

[spartaks2000]

baught second hand desktop pc, and now when i want to instal somehting it doesnt let me because im not admin(it doesnt show yes button at all) i tried chancge administration settings but, it says im logged in as user, i tried to switch accounts, but there is only one account wihtout password, please help, i dont want reinstall

 

[rgd1101]

always reinstall on a 2nd hard computer