The problem might not be related to a single problem... It could be the tube
or Hv Connector
or focus controller
or the main board
, etc etc...
If I am asked to troubleshoot this, i'll start from the Hv connector
and then Capacitors
and then FlybackILopt
, etc... and finally Main board
, this will take an extensive process and time and even if a you go for repair, technician will ask you to pay approximately $200 (including the spare parts)
and that's not worth, instead you could buy a new Lcd Monitor with that $200
but if he/she is paid less I don't think the technician will do it for you. He'll spend a lot of time and power and many equipments to test all the parts.
I would suggest you to buy a new one than getting it repaired, but it's up to you, it's only my suggestion which I think is better for you.
For your reference, I included one picture with detail description of a CRT Monitor.
I can only wish you good luck.
Thanks for using FixYa.