I had a similar problem with two different monitors..

One would 'flick on and off' when I was scrolling a web page and sometimes shut down until I did numerous on/off power button pushes then it would finally light back up but to the 'flick on/off' thing again..

I switched to a slightly newer monitor and got only the occasional 'flick on/off' but no shut down.

I checked Everest under 'display' and found a warning re: refresh rate usually being at least 85 megahertz for a classic CRT. On checking I found mine was set at 65.. I changed to 85 and the problem seems to have disappeared.

On further reflection I remembered loading some older DOS type games and wondered if this was the reason my refresh rate was changed..
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^^^
Edit .
Scrap that. My monitor has just started the old 'flick on/off' again..
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I'm assuming that power actually goes off and this is not an error code blinking on the power LED. On that assumption, logically it should be one of three potential causes:

1. The power section of the monitor is intermittent/faulty

2. The incoming power connector is insecure (that's prolly the first thing you looked at)

3. The power main plug/socket is faulty or the power cable is kinked.

The first thing I would do is borrow or use another monitor and lead and power lead to see what happens.

Thanks for the replies but I have already bought a new monitor and is working fine

Great. Then you'll be marking this thread as SOLVED!