Something has suddenly happened to my 'ageing' Canon Pixma printer. It was fine two days ago. Suddenly it had stopped printing any colour. It will only print black through it's black cartridge. I've typed a row of text selecting different colours for the words but only those in black will print. There is absolutely nothing printed for the words in colour. My first thought was maybe a clogged print head, but thought it highly unlikely that all colours would be blocked at once. The option to print in greyscale is not ticked. I've performed a few deep head cleans with no success. Any ideas?