Latitude D430 keys stuck after removing keyboard keyboar

My Latitude D430 pops up Windows shutdown menu which makes the PC unusable. I initially thought keys Ctrl + Alt + Del and Esc are stuck so I took out the keyboard, it keeps on popping up. I tried reloading Windows 7 with external keyboard but I couldn't finish cos the keys interrupts the operation.

I loaded a USB mini XP OS on it and discovered that the problem starts when the laptop runs for about 5 minutes or thereabouts.

P.S. I have stripped it down to only motherboard and it does the same thing. Any idea on what to do?