Thank you so much for your answer even if it is not good news for me
While it isn't good news (been there, done that a couple times in my life), have you learned the lesson?
My current backup solution is an 800 GB FreeNAS (BSD) server sitting on my network, in which I have each of my workstations making an hourly differential backup to (and once a month a full backup is done); this was all done using FreeNAS and the simplified backup tools on Ubuntu. Something similar could be easily done with Windows. I am currently also planning on building a 1 TB USB drive to have the FreeNAS server backup itself to on a daily basis; the server is also used as a fileserver for a variety of data that I don't want to have to reload (that took a while off the collection of CDs/DVDs I have).
Even if it is only a thumbdrive, or a second dedicated drive (internal or external), it will be worth it, no matter what the cost. The key, though, is that the backup should be automatic. If you say to yourself "I'll just back it up on occasion", you will eventually forget, or get lazy, or some other combination, and then "disaster" will hit. Trust me on this; I've seen it happen far too often to others over the decades.
Finally, when your bacon needs saving, having a backup is really nice. I once had my motherboard fail, which took my hard drive with it (the hard drive didn't fail, the data was just bad) - after buying a new motherboard and other needed items, I had my system back up and running in a few hours, with all the data (minus an hour's worth) from the backup on my server (different server - it was a custom homebrew Debian-based backup system).