I wonder if you have the correct language selected for the keyboard in your operating software.
I'm using a keyboard with both English and Bulgarian layouts on the keys. I switch between the English keyboard and the Bulgarian keyboard by clicking on the correct icon on my Task Bar. I had to set up (I'm still using XP!) the ability to use the Bulgarian keyboard through the Control Panel.
I'm sure there was a post some years back where people were having problems with typing the letters they wanted and the suggestion was to try out some of the other Cyrillic language options.
To find the language options in XP select the following icons:
Regional & Language Options