It sounds like the machine has trouble when it drops into hibernation on an automated basis. If you want to just prevent the machine from hiberating entirely, you can do this by disabling Hibernation in the Power Options icon (in Control Panel). Alternatively, you can prevent the machine from dropping into hibernation by editing the Power Schemes tab (also in Power Options); just set Hibernate to "Never" there.
Also make sure your BIOS is the most recent revision; there are some
BIOSes that have power-management bugs which needed to be corrected.
This was first published in June 2002