[Thinkpad] x220 tablet issue

[Peter Marquis-Kyle]

I sometimes dock my ThinkPad X220 Tablet in an UltraBase Series 3
connected to AC power, external display, keyboard, and mouse. In this
setup I would prefer to keep the tablet screen closed while the machine
is running.

But the computer always puts itself to sleep when I close it, even
though I have set the power options to 'Do nothing' when I close the lid.

I am running 64 bit Windows 7 Home Premium.

Can anyone here help me to fix this please?