Screen Is black on two same computers

I Have 2 dell Inspiron 1525 and I bought a Seagate 250 gb hard drive to upgrade. The droive would not work in one so I at ride the other one now both laptops do the exact same thing. They turn on all the lights flash across the board but the screen does not come on all. I have no idea what to do but if it happened to both there has to be a solution ? Please somebody helpx