How to determine why my XP system has recently decided to power itself off

My XP system, fully up to date on MS updates has decided to power off for no apparent reason. I usually leave it running 7 by 24.

I'm running Superantispyware (Thanks Broni) and AVG.

No idea if this is software or hardware caused.

Event Manager shows an error at 5:04, 'boot-start or system-start driver BEEP LBD failed to load "?

BUT not sure what that is, or if it's even relevant.

Thanks in advance for any assistance.

 

'boot-start or system-start driver BEEP LBD failed to load "
That could be the leftovers from a malware cleanup, or you may have a rootkit infection.

 

How often has it shut down?

LBD (LBD.sys) appears to be an AdAware driver (driver?). Try uninstalling AdAware (and reinstalling it if you think you need it at the present moment).