Cheap Shit
The reason you got it so cheap is because it has something seriously wrong with it and the shop owner wanted rid of it and he found a sucker to do that for him, he'll be laughing right now.
Bet he has a load of the same computers in the back store.
No matter how cheap it is, if it ain't working it's worth zilch.
You could reformat again, don't use any firewall and see what the crack is, I don't think its the firewall anyway.