how to check my c.d key?

[pistehead]

i have installed the patches for command & conquer renegade,
and have enjoyed two days playing on-line, but today when i try to play on-line i get an error message that my serial number for this product is in use by someone else,
i have read through some posts and found that i may have to re-enter my c.d key again as the last two digits might of disapeared, how do i do this please without re-installing the game,
many thanx in advance for replies,
cheers piste