Do you have multiple login's for xp, also are you using the admin account.
Ok check this registry entry,
HKEY_CURRENT_USER\Control Panel\PowerCfg - CurrentPowerPolicy, check if its set to 3 if not, do it and reboot. Here are the diff values :
- 0 = Home/Office Desk
- 1 = Portable/Laptop
- 2 = Presentation
- 3 = Always On
- 4 = Minimal Power Management
- 5 = Max Battery
so if you set it to 3 it means it is in Always ON mode.
OR, If you using xp sp2 or server 2003 there is command line utility
powercfg which can do the job. More
here.
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If your system still enters standby mode then check in your bios for power settings, change it there.
Or you can try changing the global power settings via
HKEY_USERS\.DEFAULT\Control Panel\PowerCfg.