I have restarted many times, but it never worked. Using the modern wallet, however all went fine except that I do not see my coins

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And you've copied your file "wallet date"?
When reinstalling the purse, the old file is replaced.
Yes I did that. I made thre copies in three different locations and I extracted the private key in case of the worst.
Edit : after a really long time of wait, I managed to get the full chain downloaded. I then imported my private key and now it works

!