No input in dos programs (winXP)

[Luiz Fernando Mendonca]

Hi there.
I have a really annoying problem, where if I start dos games/apps from
shortcuts, they take no input from mouse or keyboard.
If I start cmd.exe, then execute the game/app, then I get input, BUT if
the app/game goes full screen (cos I pressed alt+enter or cos it went into
graph mode or something) then I get no input, and even if I press alt+enter
for it to come back to window mode, I still get not input.
When they go full screen due to graph mode, then it seems like it also
freezes after 1 or 2 seconds (altho I cannot confirm that its not the app's
own problem this; altho I find it unlikelly).

Is there a way for me to restore the whole dos emulator or all the files
that cmd uses or something from the cd? Or from another winXP machine?

Btw, I can't tell how or when this started, because it's been a long
time since my last format and I've only noticed this recently when I tried
to play a couple of old dos games.

My system:
AthlonXP 1800+
512ddr
Primary partition: 12gb total: 4gb free.
WinXP Pro sp1 +all win updates
DirectX 9
WMP 9

Thanks in advance.
Luiz F Mendonca.