You mentioned that when you us any of the Ctrl+Alt+ Fn keys you are taken to a virtual console.
The one you need is: Ctrl+Alt+ F8.
You might want to check your keyboard and see if it has a key to activate/change the function of the Fn keys. My Microsoft ergo natural 4000 has a "F Lock" key that changes the Fn key function. If you have the same, you may think you are hitting the proper key strokes but in actuality its different. Similar to typing a password and the system says its not the right password, then you notice your CAPS Lock is on.
If the above doesn't work, something may have borked up on you system. If you know the list of processes that run, when your system is running properly, you can look through your process list and make sure all the necessary processes are running when you have this problem.
You also mentioned that: " press Ctrl+D or logout. But doing that leaves me in virtual console itself in the login prompt." Does this also mean that you can no longer boot your system to a gui?
What version of PCLOS are you using? What DE(kde, gnome,...)?