If i use recovery disk it won't ask me to write the number once again? if so i will need it - and there the problem begins.
If you use recovery disc you will not be asked to enter product key. Original recovery image that you got with your notebook is already activated. You can use this disc 1000 times and every time OS will be activated properly.
Just in case that you want to install OS using original Microsoft installation disc you need valid product key for OS activation.
If you have more questions you are welcome.