Some of the most popular Android smartphone apps are these "task killer" apps that stop tasks and apps that are running in the background and eating up your device's memory. I had been running Advanced Task Killer (ATK) for a number of years but I recently deleted this app from my smartphone. Here's why: my on-screen keyboard would stop entering data. The keyboard would look like it's accepting my touch-based input, but no letters would appear.
When I did some searching online to see why my HTC ThunderBolt's keyboard had stopped working, I discovered that other people had experienced similar issues if they had ATK or other similar apps installed on their devices. I've had my ThunderBolt for over a year and I had never had this happen before. ATK had been running without any issues (and I did not enable task autokilling), so I wasn't sure why my phone suddenly started acting this way.
One possible remedy would be to perform a hard reset and erase everything on my device.
The other solution: uninstall ATK, reboot, and everything should be fine. I went with this option and my phone has been working fine ever since.
If you're an Android user, you probably have ATK or a similar task killer running on your device. I would suggest that you remove this app and reboot your device so that you don't face possible on-screen keyboard problems in the future.