First of all your a noob and have 0 experience. You will probably need help getting your first computers running. You can never sell as cheap as Dell ect....., why on earth would anyone buy a PC from you with no warranty, and no support, when they can buy from Dell ect..., and get a 3year warranty with support.
2nd the competition is steep on Ebay, I been trying to profit selling computers on Ebay for 2 years, I sell a few here and there, but it sure dont pay the bills.
Look at Ebays advanced auctions and see whats selling, and see if you can do it that cheap with free shippipng, and after fees. Also if you have no warranty support, you just shot yourself in the foot.
Your better of working at McDonalds.
Your fees are off, you forgot to add Paypal Fees, and shipping fees. Bye Bye profit. Also just so you know, no one will buy from you without a high feedback rating, and Ebay considers computers high risk items, and will put your funds on hold until you get positive feedback, or 27 days, or you can prove it has been delivered. So if your planning on selling and using the money to buy parts, forget it. The money will be tied up.
And when you get bad feedback from shipping a DOA PC, "it happens" or for bad support, you will get no sales once the feedback dips under 98% +