Norton Family doesn't accept my pc

Once I installed Norton Family on my pc, created a NF account online, etc. and the app worked perfect.

Unfortunately later I had to reinstall my pc (Win xp) therefore I had to install Norton Family again. The installation was ok on the pc. From N. Family account side child added again, device added again. But I can not finish the set up from the child side. When I log into the pc with my childs login, a box appeares for parental Norton Family log in. Logging in as a parent, it requires adding a device. When I accept the defaultly offered device, my pc, it says the device is already added, and I should add an other device. The child monitoring is not functioning now.

What shall I do?

Thanks for your help in advance.