I've been experiencing problems for a week now in that sometimes the colours on my desktop picture aren't right, I also get clicking noise on monitor when STARTING up computer, blank screen and green light keeps going on and off until I've pressed button a few times when it seems to right itself and screen comes on.  TODAY my desktop icons had been rearranged, the icon and print size has suddenly decreased, and everything on the screen has moved right over to the left.  I really don't know WHETHER it's the monitor or computer itself and would appreciate some advice.  Thanks.Please give more details.
It could be either the video card, the monitor, or even the cable.
Is the cable a VGA type? A loose connector can give symptoms like you mentioned.

Lost icon positions INDICATE the system lost track of what size screen your have.
what's the age?

desktop icon location can change when the video card updates and the resolution changes.
sounds like the video card is not quite right - time for a new one perhaps?
is it built-in or an add-on type card?

had the pictures on the screen always looked like crap or is this a recent issue?
I know some photographers who always complain about the colours of pictures on their screens until they went out and coughed up serious money for a decent monitor.The problems started just after a Windows update, probably coincidentally.  The desktop colour changed from blue to red/orange and everything flickered but okay after restarting computer.  Two days later the icons changed place and size.  The cables all seem to be secure.   Have tried switching monitor off for a minute when it starts clicking which seems to clear it.  The screen then shows 'no input' message for a few seconds and then comes on okay. 
The monitor and Windows 7 program are about 3 years old. 
It sounds from your replies as THOUGH there's more to it than just a faulty monitor and I don't know anything about video cards so it looks like I'll be paying a visit to our local computer shop! 
 Before you go to the shop and spend money can you borrow another monitor and hook it up to test ? ?

As always troubleshooting is a step by step process...and thats what i would start with.