HDD replacement and o/s activation problem

Hi all,

           Hope some one can help me, got a problem with my laptop after replacing the original HDD after it died.

          Replaced the drive easy enough, installed win vista ultimate on new drive (original HDD ran Win xp home), up and running no problems all features OK.

          Now comes the problem, without warning the software was asking to be activated.

          Well i thought by typing in the serial from the box was doing just that?

          The software will not allow me to open any programs what so ever, not even the start menu. All i get is a window telling me to enter the activation key, or online purchase browser.

             Now as my copy of win Vista is a real version (not a copy) the number on the box should work for more than a couple of weeks, but when i re enter the number, i get an error message stating the bios license is wrong.

can any one give me any help on this?

Many Thanks