my date on my computer was wrong when my windows updated

my computer was telling me to update my computer and i did and then it told me to restart my computer and little did i know that my date was set wrong on my computer and when i restarted it thats when it told me that i was a vitim of counterfiet for this software...... how do i fix i??? this is a rebuilt computer i bought from someone 4 months ago..how can i fix this... i dont wanna be involved with anything counterfiet.. so someone please help me