backup dosbox directories, completely uninstall, verify the dosbox configuration files are all removed, then reinstall.

Thanks for your help but I've already tried that without any success including manually deleting the configuration files saved in the appdata\local\DOSbox directory.

Describe your troubleshooting steps which may save time, such as your attempt above.

Try output=overlay. If you are unfamiliar with dosbox configuration, then there is documentation on changing output modes. The output mode change isn't a solution, but instead is a test to try.

Also, at windows command prompt, could try this:
set sdl_videodriver=windib
dosbox.exe

Where your current working directory is the dosbox directory.

Thanks, so I have uninstalled dosbox completely and made sure that any config files for dosbox in the dosbox folder have been removed. I have also made sure that there are no dosbox config files saved in the user directory i.e. c:\users\username\appdata\local\dosbox\. I have then reinstalled Dosbox from scratch but when I run it I have the same problem as before in that no keyboard input is recognised at the prompt z:\>. I should point out that it is all keyboard input that is no recognised and not just particular keys as has been described by others previously. At the sametime Dosbox special key combinations for altering the CPU cycles such as Ctrl+F11 or Ctrl+F12 and CTrl+F1 (keyboard mapper) are no recognised. If I start dosbox and set the config file so that it run a program once dosbox opens the program will run but mouse input is fine but again the keyboard is not recognised.

As suggested I have altered my config file to change the output=overlay but this has not made a difference and unfortunately trying to set sdl_videodriver=windib then running
dosbox does not resolve the problem either. I guess it may be that I have come across an obscure bug which has been resolved (unintentional?) by one of the unofficial builds.

Hi again, I seem to have got keyboard input being recognised by DOSbox now.

To get things working I needed to disable the OSD (On screen display program) that is installed by my laptop manufacturer (Alienware) and is used to display on screen notifications. Then at the windows command prompt do:
set sdl_videodriver=windib
dosbox.exe

However, if I do not do all of these things (i.e. disable OSD and set sdl_videodriver) the problem I described previously reoccurs. Strange how this problem has only developed at some point in the last few months.

Anyway, just like to say thanks to truth5678 for your help.

That's good news. 😀 You may search for other Alienware specific software/drivers which load on computer startup. Also, try disabling Windows 7 desktop composition and any other associated services which affect the desktop. That latter issue has been reported repeatedly and seems like a faster way to deprecate software than the old fashioned way of deprecating APIs.

I had same problem, the problem was an anti keylogging service called ENTRY PROJECT by SENTRY BAY witch is encluded with AOL SHIELD turn it off in msconfig. games now work great