2 shorts beeps and a black screen

Hello,
I need help. I recently took out my hard drive in my hp laptop to replace, only to find the guy sold me the wrong one. so I went to put back in the old one, got it all in there, turned on the computer and it just beeps 2 short beeps and nothing else. the fans are goin, black screen, and thats it. I put in a 2nd ram card, but even tried with just one and same thing happened.....help me!