Hibernation and Standby locks up

I have a Sony Vaio laptop (built in 2002) that locks up whenever I attempt to go into either Standby or Hibernation modes. I’ve reformatted the entire system, and both work fine…for a while. Then it starts all over again. I have also noticed that if I create a new user account, SOMETIMES both will work; most of the time, they don’t. Any ideas?