Pode ser uma questão da fonte de alimentação estar com defeito e enviar sinais falsos de energia quando a energia é perturbada.
O seu computador está desligado ou está em hibernação? Houve um problema semelhante mencionado aqui :
A program can tell Vista wait a certain period of time and then invoke some executable code at an address the program provides. An example is if you use a program like Microsoft's Outlook email client where you can set a reminder task for a future date and time. Outlook tells Vista to wait X amount of time and then execute some Outlook code. That Outlook code then displays your reminder.
But what happens if you put your computer to sleep or into hibernation? Well, before Vista you wouldn't get your reminder. Or maybe your anti-virus scan wouldn't happen. Or maybe Windows Update wouldn't run. Vista changed all that.
When Vista goes to sleep or into hibernation it first checks to see if there are any timers set to go off. If there is, it takes the next timer set to go off and sets an alarm in the platform hardware for that day and time. In the hardware this is typically an alarm that's part of the real time clock (RTC). Once Vista sets the RTC alarm it goes to sleep or into hibernation.
When the RTC alarm goes off your system turns on. Vista resumes and is notified of the alarm having gone off. Vista checks its timer list and executes the code associated with the timer that when off. When the code is done executing Vista will go back to sleep after two minutes of idle time.