saturn playing up

right just latley my saturn wont load my crashes constantly on the boot up screen,the bit where all the triangles form the sega sat logo just does it on all my games.and they aint scratched or anything like that.any ideas what i could od to rectify it.also another strange thing,if i leave the saturn switched on for like 1 seems to work ok.but switch it off,leave it to cool down,it has same problems again,not booting.