Can not have a file name with "s"

I formatted my hdd last weekend and I just experienced a strange thing: when I want to rename a file, I am unable to use letter "s" which works perfectly well elsewhere. It does that with the "s" and, regardless of the file extension. Moreover, I can type a file name containing an "s" in Word, make a paste and file name is accepted. I looked on Google and I found nothing. I prefer to ask here if this is a virus, that I find it strange ... What do you think?

Do you have an error message or letter does not appear? Have you tried with a command prompt? with total order or other substitutes to explore?

The letter does not simply appear. I do not know the command prompt, I'll try to see how it works and I wish you know. Thank you!

You'd probably blocked some key. Just check that in your settings in control panel.

In the command prompt, it works well. I will definitely look at the settings.