Mac crashing when waking from sleep

Recently my mac's been having some trouble, which is running 10.6.8. Everytime I wake it from sleep, whether it's for 8 hours or 3 minutes, there's a chance that it will simply crash. I open it up, a quick flash of light, then silence. I have to press the power button twice every time in order for it to register, and even then there's a chance it'll simply crash again. Only after about 5 times of crashing and rebooting will it finally reboot all the way. I've lost papers and notes due to this and would love to know what's wrong with it.