We have to get to the bottom of this - we need to get you back to building
I'm going to assume this is the airbrush kit you have:
http://www.machinemart.co.uk/shop/product/details/pro-air-brush-kit-cab2pIf that is the case, let's start going through this methodically.
From your statement and other comments, maybe the problem isn't in the airbrush at all but in the pickup tube of the color cup. If the color cup is metal, let's try soaking it in some solvent (prefer lacquer thinner as this will be guaranteed to dissolve all paint types). Once you have soaked it a decent while, grab some pipe cleaners and use them down in the pipe of the color tube, let's make sure there is no paint in there creating a blockage.
If you have the siphon jar too, go through a similar procedure to make sure the pickup tube isn't blocked in that one too.
Next is check the needle to make sure it's not bent towards the tip.
If you're using the siphon jar and experiencing the issue, check the vent hole in the lid isn't blocked - if it is this will stop the airbrush from being able to suck up paint.
Please post back with any findings or progress - I will keep brainstorming in the mean time to see if I can think of anything else worth checking.
Ray