I have the same problem, but with papers.
With exams I suggest you go to a place where you can't help but study; like a library. Mine's full of drunken Frenchmen and Atlantic whores! Drink plenty of energy drinks. Do jumping jacks when studying at home.
crap I'm really drunk...
if studying at home, turn off the fuckin PC, UNPLUG IT. Also listen to Bach, I find it helps sometimes,