For everything else you would have to provide at least some useful information. Just saying that printing doesn't work is not particularly sensible when you don't tell us anything about your printer, your documents, print settings etc..
Sorry, but you are quite right! I do not know how or why everything got back to normal after i rebooted my Mac!
My problem was that I could not make any selections for size of print as it stuck at 6X4 while I was trying to get A4 size print.
And thanks for the reference provided. I have saved it in case of any future problems, although I will try all usual ways of getting back to normal first before jumping to conclusions! And the forum is excellent!