It would have helped if you had stated model/make of printer, then if other ABers have same printer they can help you a lot better than I can.
It looks like your printer heads are blocked and need cleaning. Go into your printer details and look for maintenance then delve in there to see how to clean etc.
It is an epson c20, and so far I have been advised to scrap, change or steam-clean it! Though I would like to know the why's and wherefor's to this problem and to what causes it.thanx in advance
The print heads can get clogged by the ink drying out if machine is left on and not used (similar to leaving cap off fountain pen) or by not being used for a while. Refer to 'Printing Problems' in your manual or look here: