Normaly water comes from the tap and you push down on a metal tube to make water come from the shower head and back etc now it won't go back to the tap its just stayed coming from the shower head ?

Assuming you are speaking about a diverter on tub spout. Sounds like knob and stem have broken from diverter valve in spout. No repair. Replace tub spout. Spouts not that expensive.

The "tube" you push down on, is it on the top of the tub sppout like this one? Danze 8 Wall Mount Tub Spout W Diverter Brushed Nickel (http://www.google.com/products/catalog?hl=en&wrapid=tlif129599921602310&q=tub+spout+w/diverter&um=1&ie=UTF-8&cid=15887396114880875253&ei=92A_TfjWAsT_lgen1KCMAw&sa=X&oi=product_catalog_result&ct=image&resnum=7&ved=0CEUQ8gIwBg#) If so just give it a good smack with the heel of your shoe, not while on your foot of course. If this does "fix" the problem them replacing the spout is cheap and easy like Harold said. Souts either slip on with a set screw on the bottom or they are threaed on. You have to find out which one you have before trying to replace. Replacing a Tub Spout (http://plumbing.about.com/od/diypluming/ss/Tubspout.htm)