Lost Key ( Password ) of norton anivirus after restore of the whole computer system,

Hey 

I lost the key ( Passwor) of my norton antivirus after resotoring the whole PC-system?

Should i buy a new Antivirus product?  or is there any cheaper solution, because my antivirus ends up at the end of  this year, so i still have time which i dont want to lose. Thx for your support :)