Windows 7 activation help

Hi, my friend let me use a old windows disk so I could try out windows 7. After using it for a few months with it being unactivated it gave me the black screen and told me my trial was over. I went out and ordered windows 7 and planned on just putting in the activation key and being ready to go considering I already had windows downloaded. This way I wouldn't have to go through the hassle of trying to download windows on a computer that just shows a black screen. I made sure I bought the same exact copy of windows already downloaded on my computer ( OEM 64 bit SP1 windows 7 proffesional) once I got my key I put it in and I got the activation successful window but then nothing changed and I still have a black screen even after restarting my computer. Can anyone please help me fix this?

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