Its (normally) at 75Hx 1024x768.
You cant really degauss an LCD but you can auto detect or reset the screen etc.
I have another full PC to test this on and swapping monitors between them showed that there was nothing wrong with either monitor or graphics card. However after the test, just randomly maybe 4 hours later, it happened again.
My graphics card is dual output so I have put the 2nd monitor on at the same time and at the moment all I can do is wait until it happens again and see if both monitors do it or just the one.
Unfortunately it is a Sony LCD which is out of warranty, if not by far.
Was just wondering what people thought. Another thing, I would find it difficult to prove that it was faulty if I were to try for an RMA...