Was it running fine for your friend before you got it? Are you getting any image at all when you first turn it on, or any sound?
are your motherboard's specs. If you got RAM that isn't 553MHz or 667MHz that may be messing it up. Is it 2x 1GB modules, because if its just 1x 2GB module that may be messing it up. Is everything plugged in? Sounds silly but not uncommon to forget the 4 or 8-pin plug by the CPU.
Also, are you using your friends Windows license? Its an HP pre-built motherboard, so the old Windows OEM license is tied to it. Unless you did a clean install of a new copy.
Please read through the thread thoroughly before responding.
Nobody wants to read a wall of text, formatting is your friend.
i5 3570k | 8GB G.Skill 1600MHz | R9 290 | SeaSonic 750X