OH... MY... GOD...
This problem really shook me up bad. I spent the whole night doing everything written in this article but NO RESULT.
Eventually, THIS HELPED, and I was able to see my iphone in my iTunes :
1. I uninstalled and deleted all and every traces of iTunes and Apple related anything from the Control Panel.
2. Deleted all Apple related folders from Program Files.
3. Downloaded an older version of iTunes from here (the oldest I could see) : Troubleshooting issues with iTunes for Windows updates
4. Started this old version of iTunes, though it would not start saying that the iTunes Library can't be imported as it was created using a later version of iTunes (understandable).
5. Uninstalled this older version (11 something) from computer and again deleted all Apple related files and folders I could find in Control Panel and Program Files.
6. Restarted my computer.
7. Installed latest version of iTunes (in my case 64 bit) - guys, you have to see which version would go with your machine, 32bit, 64 bit, or 64 bit with old video card (applicable in some older laptops and desktops).
8. Restarted my computer. Did not run iTunes at this stage, only started the computer.
9. Attached my iphone to allow it to install the needed connectivity files (automatic process).
10. Made sure my iphone was visible in explorer as a device. Unlocked it and 'Trusted' my computer.
11. Started iTunes, and Lo & Behold, my iphone was visible there, so I could back up, add more music etc.
Hope it would help someone like me.
P.S. As much as I LOVE my iDevices (iPhone, iPad, iPod), I absolutely HATE, DETEST, ABHOR the iTunes. For Heavens sake Apple, why did the interface between humans and iDevices HAD TO BE through iTunes, and why it couldn't be a user-friendly interface???