5 minutes ago I finished editing bass track in Cakewalk and I just wanted to save the project (overwrite the previous project file) but the pop up menu appeared "Can not write file". I have 33GB of space on my SSD drive so the lack of space couldn't be the case here. I tried saving in a different folder - the files finished copying and everything seemed to be ok but then suddenly I see that it didn't save the project again. So I tried saving the project again in original project audio folder but it didn't help as well. So I said "screw it" and I closed the project. Next I open the cakewalk again and see that my project (called fuzz song 1.1) disappeared!!! Not only my recent work couldn't be saved but all of my work is now erased!!! How can I find/restore my original project file?

Is your original project folder still there?  You could look in its Audio folder and import/copy/paste all the audio files into a new project to rebuild it.  But I'm thinking your project must be somewhere if you saved it several times?  Have you searched for the file name across all your drives?

Never heard of such a thing, but if the original file has really been deleted somehow, and you don't have a recent backup, try 'Recuva' or equivalent 3rd-party file recovery utility.

In such inexplicable, weird problem situations I've sometimes found it can be useful just to let the PC be for several minutes before trying to re-save or do any rescue operations. My CW-tools are antique, but also my laptop sometimes just needs to "think it through properly". I have no idea whats's happening inside the system in those situations, but sometimes it's been worth waiting.