My sisters pc is playing up! At night she puts it on stand by, turns the monitor off and goes to bed. The next morning when she goes downstairs it has woken itself up and is ready for her to log on, with out her having to do anything. I can't help her as I have a mac and am not familar with Windows set up. Thanks.
Not that this will help much.. but my Laptop went thru a phase of turning itself back on from standby when for months and months before it was fine... no idea why the sudden change, maybe it felt neglected.. In the end, I threw it down the stairs and bought a new one. Problem fixed...... sort of.
vehelpfulguy's answer should help - some cable providers are known to send a wake-on-lan request - if you're not happy fiddling with the BIOS, try unplugging your network cable and see if the problem disappears.