Drivers and utilities for Sony Vaio VGN-FE770G
There are 2 ms updates under Windows operating system that are related to power management and standby features and that need to be installed if the system was reinstalled using a retail CD. Check in add/remove programs whether they're already installed (tick the show update box at the top), else install them. The sony notebook utility could also be needed. Also note that XP Pro and XP Home aren't listed as compatible OS, according to Sony's website that model should have come with XP Media Center Edition.
If the laptop came with XP Home or MCE and XP Pro was reinstalled from scratch she may have forgotten to reinstall the proper driver for some hardware device (chispet, sound, network, video, card reader, touchpad, ...). Check the device manager and update the drivers when a new version has been released. Wrong or outdated drivers will cause issues with standby options.
While you're in the device manager you could also check the power management tab of each device that has one, the "Allow the computer to turn off this device to save power" option should be ticked for all network adapters and all usb hubs. If you find a device that has the power management tab and where the option is greyed out it could be the one causing your troubles.
If you were able to change the standby time using powercfg it's already good news. A complete system restore using the recovery partition or the original CD would almost certainly solve the problem but that's a last resort solution, if it happened on my computer I think I'd rather live with no power options.
To stay on the safe side I would backup the registry with
erunt and create a system restore point manually (all programs => accessories => system tools => system restore) before applying any update or uninstalling/reinstalling any driver.
Keep us posted.