16bit Command Line Application Ignores Keyboard Input

Our company has a 16bit command line application that works fine under XP and was working fine under Vista until, we believe, service pack 1 was installed. The program works initially to accept keyboard input but seems to ignore any keyboard input after a few minutes of the PC being left with no activity. We have tested this on Windows Vista and Windows 7 and have exactly the same issue. We have created a very basic program that would allow you to type characters and exit when Enter is pressed. I have narrowed the time delay before the program freezes down to about 4 minutes of inactivity. This will cause the program to not respond to any key presses on the keyboard and has to be closed by clicking on the x in the top right corner.

I am wondering if anyone else is having this issue and also if there is a fix for this? (Perhaps a registry key timeout setting?) Below is a copy of the source code we used for our simple program. The program is written in Microsoft C version 5. We are using an Int 16h Function 00h BIOS call to read the keyboard character.