The few disks he tried came with a Philips MSX2, which are 128K machines. And typical software that came with those machines, is designed for 128K MSX2's. So it's quite possible there's nothing wrong with the drives and it's just software not working. Or 20+ year old disks that became unreadable.
The usual way to check would be to format a few disks. Which he can't do because he doesn't have a keyboard to type _FORMAT on. 
Or to fresh format disks on a PC and write some disk images to. Which he has yet to figure out how to do that, and whether that works at all.
Just file transfer would be easy: format a 720K disk on PC, boot MSX, insert disk, type commands to run stuff (in that order). Which won't work due to lack of keyboard. The other way: format a 720K disk on PC, add files to make it auto-run, insert disk in MSX, reset, won't work either because the PC bootsector code makes an MSX choke during boot. So it's either: [boot MSX, insert PC formatted floppy, type] or [format disk on MSX, use PC to copy files onto it, boot MSX with that].
Because it makes EVERYTHING ELSE so extremely difficult, I can only suggest Luca that he focusses on sorting out the keyboard problem first (btw did you ask seller what happened to original keyboard? Even just the connector would be useful). And if possible: spend some time with emulators, to learn BASIC commands, how to use floppies, files, MSX-DOS commands, etc.
In the mean time, it wouldn't be a bad idea to obtain a simple digital multimeter (no special requirements, a € 20 thingie from hardware store should do), and a soldering iron (15~25W, definitely not more than that). Those 2 items are sure to come in handy, and unless he can find someone to do it for him, he'll have to learn some basics on how to use them. For either tool, not difficult even for absolute beginners.
So Luca made things very difficult for himself by getting an MSX that comes without a keyboard, a very rare model at that, not knowing the MSX system, AND doing that not knowing much about hardware either.
If you press CTRL when booting, (..)
See above.
I preferrred DCOPY back in the days, easy to use & does the job. But it's a DOS program, how it works under Windows 2000 or later? (if anyone knows for sure, plz. share). These days I'd use Linux "dd" tool. Just as easy to use as DCOPY, if you can use Linux 
(for example CD-bootable Puppy Linux would do the job).
Single sided (360K) disks are problematic to write on PC, because it's not a format that PC's recognize (all 360K formats known on PC are double sided with fewer tracks). So even if the write goes ahead the produced floppy may contain garbage.
Easier is to transfer 360K disk images on a 720K disk, and write the 360K disk on the MSX. For the time being, I suggest limiting yourself to the 720K ones... 
DCOPY works fine with Windows 7 32bit. I've also created sucessfully 360KB disks by means of a USB external drive and Disk-Manager 
Just write a real disk with your PC with a disk image with a nice MSX2 game with FM and run it. E.g. Psycho World is a good one
