You can shine a light through it and determine whether it's
the backlight or lcd itself that's blanked.

wrote:
Hi,

I recently bought a Dell 19" tft monitor. I noticed after using it for
a while it would periodically blank for several seconds, then return to
normal. This weekend however, it blanked and the only way to resolve it
was to switch off the monitor for 20 minutes. It did this 3 times on
Saturday. When it does this, the monitor is still receiving a signal
from the PC, but the screen is completely black.
Any ideas what could be causing the problem here? As it's intermittent,
I want to avoid sending it back to the supplier, only for them to say
they can't reproduce the problem. Are there any diagnostics I can run
on the monitor myself?

Thanks.
Andrew.