Ok so i have my eye on a second hand Mac mini to keep my kids of my mac ....
Can you believe kids these days 5 and 7 and they use it more than me but i am worried about them messing my stuff up..So getting back to my point the Mac mini second hand from Ebay i assume will come with sellers key ring lock on ...How do i get rid of all his stuff including his passwords and reset them to mine ?

Also can i run this on my small LCD TV screen ??? If not what should i be looking for ?