unattended Power-on

I have put Win7 [Version 6.1.7000] on my Asus W7J laptop, it was running vista fine - but slow.. now i get the laptop powering on overnight after ive put it into sleep, and find it has hung with a black screen and no keyboard activity in the morning. I have to power it down and reboot - its very annoying and very loud - the fans are running full speed when its hanging.

Any thoughts what might be causing this ?

What are the specifications of your computer? Sounds like a problem with the graphics card to me.