Resolve The Error 912 - <b> The computer has been removed</b> in the HP Compaq dx2700 MT

On the Desktop computer HP Compaq dx 2700, after opening the cover of CPU case (altough it has been closed back again), when starting the computer, there will be the alarm tone sound is quite disturbing.
And we must press the F1 key to continue loading the OS (Operating System). And this will continue on every time the computer is restarted.

The warning is : error 912 - The computer has been removed. The machinecover has been removed
since last system start up. please Ensure That any system access wasauthorized.

To solve this problem:
• Turn the computer on
• Press F10 to enter the BIOS setup, wait for about 10 seconds
• Find the Hardware Monitor Setup menu (use arrow keys), select then press enter
• On Reset Case Open Status, change value from Disable to Enable (use + on the numeric pad on the right side of the keyboard to change the value)