When i switch off my computer the screen wont switch off!?

Question

the screen just flashes with reds white blues &black, the only way to close it down is to switch off the main power.

Answer 1

It is sensible to plug the computer, screen etc into a 4 way suppressor block and turn of the plug on the wall when not in use. This will force all components off and save electricity as otherwise the monitor will usually draw current in standby mode http://www.trilogicuk.co.uk

Answer 2

Unless this is a laptop, power to the monitor is independent of the PC power.  You need to power down both (or use the power strip) in order to shut down the monitor,

Monitors that are energy-star compliant should switch to standby mode when the PC goes off - sounds like yours is not compliant. The flashing colors are a test pattern generated by the monitor,