Thank you for your suggestions. The problem is resolved finally!
When I installed one of the softwares, it must have actually installed or changed the language settings . . . and that actually was probably the reason behind this issue I had.
Thank you for your help. After making sure the language setting was only for Western Europe and US, I went back to the Display Properties and set it back to the default Windows Standard setting. It worked after a few attempts only (?!)... but it worked.... :-)