What you mean by negative profit? If I am getting electricity for free, then there will be no loss, right? Anyway, I don't care if I get any profit or not. Mining will be fun, and I want to experience it.
I mean that mining with a good, new i7 + decent GPU PC 24/7 will net you less than a dollar a year at current diff, block reward and BTC price.
Even if you get free electricity, i doubt that you'd find a free PC + network equipment + ISP + power for $0 a year. As soon as you pay $10 for a new power cable or a new PC keyboard, you'll never be able to recuperate this cost by mining, hence you'll make a negative profit.
As soon as you decide to mine with an old "free" PC, do realise that you won't even come close to $1/year... It'll probably only be a small fraction of this.
Next to this, the concept of "free" power is pretty confusing. Either you're stealing power, or somebody is paying for it... Either you yourself (maybe it's calculated into your monthly rent), maybe your parents, maybe your employer,... But somebody is footing the bill, and one way or another, most of the time, the bill is passed on to you (maybe your parents make you do chores, maybe your employer sees your power consumption as part of your salary, maybe your rent gets higher after a couple of years because the landlord pays so much for his power bill,...).