I have created the watch only wallet just to try to see my old transaction that i lost track with.
After that, I generated a Receive address from this wallet to Coinbase, i made a transfer from Coinbase.
What do you mean with "lost track" with your old transaction? Was it a Bitcoin Core wallet? And if it was, what happened to it? Do you still have access to that wallet?
Where was the wallet you used to get that address?
Please answer these questions.
(they say i need a private key to sweep but i don't have a clue where i can find that)
You do. Without the private-key, all you can do is watch the wallet (thus why it is called a "watch-only" wallet).
Ok, i thought this could be a long story that could discourage you ^^
1/ I have some bitcoins sent to my bitcoin core from coinbase to a whole new bitcoin core wallet on my laptop
2/ i realised that i don't have enough space on my laptop, so i tried to migrate it to an external disk
3/ Done, the sync continue but it takes forever ! So i decided to migrate this "bitcoin" folder on my disk to my big computer which has more space and more power by replacing the whole bitcoin folder (with the wallet.dat inside)
4/ Sync continues and finished but no balance.
5/ I don't know how to trace it so read some internet advice to install electrum and import the address.
6/ which made me create a Watch only wallet.
7/ since I need some bitcoin i was saying that while waiting to solve this, i can send some more from coinbase to this brand new wallet to use them. But totally zapped the fact that i was using a Watch Only wallet.
Now i'm stuck again.
Voilà i hope i made myself clear. Thanks a lot Smiley