Does setting your PC in the "sleep mode" overnight (with windows 7 power options") cause the same "thermal stres" to your PC as actually shutting down the PC and booring it back up in the morning ?

Anything left on with power becomes a potential fire hazard and that is the only real reason you should shut down your PC completely during sleep hours. Even a few Xbox 360s have caused fires because people left them on unattended.

I never thought of a fire ! I have been gaming for over 40 years and never had a fire issue(maybe lucky).
My main Q was if the "sleep mode" causes the same thermal stress that a complete shut down and boot up does on the PS system ?
Thanks

No, low power state would be very low heat output but the potential for a short in the PSU is still there. Sure, most people will never have a fire happen but it has happened is my point. We all know about laptop batteries causing fires, right? I've read of overclockers having their PC catch fire more than once too.

Yes. On Windows, at least, sleep essentially shuts off the computer except for the RAM. With hibernation, the computer does shut down totally but the contents of RAM are written to the hard drive, so when the computer is powered back on it resumes what you were doing.

IMO, there's not much reason to worry about shutting a PC down at night. If you're concerned about power usage, use sleep or hibernation. And there's no reason to leave monitors on. Let the OS power them down after 15-20 minutes.

I think hibernation mode requires .5 volt.

Like many (most?) other pieces of modern electronic hardware, a computer will draw a small amount of power even when turned off - unless you unplug it or flip the switch on the PSU.

I have all the PC stuff (PC, Amplifier of the surroundsystem, router, printer) plugged into one multi-outlet power strip (this is from babelfish, I hope you understand) with a switch. Same for my TV, Hifi, DVD etc.

When I go to bed, I switch all of it off, only switching it back on in the evening when I come back home from work. Saves me around 70 to 90 € a year on electricity costs.