my desktop computer has started to start up on its own at various times of day after being shut down . Any ideas as to why ?

Ron d, February 2011

There are also some other wakeups/power up options. You may have:
Powerup/wakeups on lan
Powerup/wakeups on key press
Powerup/wakeups on modem
Powerup/wakeups on mouse
Powerup/wakeups on «some other event»
Powerup/wakeups at time/day/date

On some rare occasions, like some random electrical glitch, one of those settings could become enabled.

On boot, enter your BIOS setup.
Make sure that none of those are enabled. Deactivate any that is active.

Electro, April 2011

you may have put your windows pc into sleep mode where it will wake up if things are cponnected or mouse moved etc. ensure you choose shut down. also search "wake up on lan" in help to make sure you have this turned off.

Hengist The Nord, February 2011