I've just bought a Sony monitor. But after a few days the screen turned black for a few seconds when I was working on my computer. It has happened several times now. Recently the monitor broke down for half an hour, the green powerlight was out. I tried to unplug the electricity cable and then replug it, but it didn't work. I haven't moved the screen so I don't think the cable has fallen out or moved. Once I couldn't even turn it on while starting my pc I had to wait 15 min and then suddenly the monitor was turned on.
Maybe the electricity cable isn't working properly coz the powerlight isn't on when I have the problem.
Does anyone know what the problem is?

Hi BlueMouse!
Welcome to http://www.pcguide.com/ubb/pcgubb.gif forums.

Sounds like your Monitor is on the "blink" more than anything else. Is there any panel light at all on when it's not working? Is your monitor and computer both plugged into the same surge protector? (If you don't have a surge protector, you should:))
Just to be sure, I would shut down your system, unplug your computer and monitor.
First, be sure that the power cord is plugged firmly into the back of your monitor. (Unless of course it's the type that comes directly out of the monitor and can't be removed)
Second, be sure that the cable from your video card on your computer to the monitor is also fully inserted at both ends.There are some "Thumb screws" usually that hold this cable in place.
A sure fire test would be, if possible, to try your monitor on a different computer)Or try a different monitor on your computer. :)
The "good" news is, that since it's a brand new monitor- You should be able to get a replacement at the store where you purchased it.

Good luck!