Start your computer, during bios loading press F8 repeatedly. You'll gone see in next screen few option to start your computer. Choose "Last known good configuration" and press enter, from next screen choose a restore point before service pack update was installed and follow the steps from that window, after that you'll gone have your computer restored. This in case you don't have system restore closed. If this is not work write a message and i'll give you another method to repair your computer a litlle bit heavier.
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Start your computer, during bios loading press F8 repeatedly. You'll gone see in next screen few option to start your computer. Choose "Last known good configuration" and press enter, from next screen choose a restore point before service pack update was installed and follow the steps from that window, after that you'll gone have your computer restored. This in case you don't have system restore closed. If this is not work write a message and i'll give you another method to repair your computer a litlle bit heavier.