CPU too hot

When my iMac G5 works in a very intensive way, it switch suddely in the sleep mode.
Thierry Mella wrote on :

Hi,

iMac G5 + Leopard 10.5.6

When my iMac G5 works in a very intensive way, it switch suddely in the sleep mode.

It didn't happend under Panther 10.3.9

I think it happend because the CPU is too hot.

Do you know if it's possible to stop this switch ?

TIA,

Thierry