If you can't use windows "shut down" selection, then you may need to reposition the power switch lead on the motherboard, or do a fresh windows installation. I also found that some boards don't shut down right using sleep mode. Even a weak power supply should shut down easily; it's the powering on that may be a problem.
Well I can't do a fresh window installation because I get the video signal to the monitors. THis all started when I was browsing the internet and all of the sudden the screens went black. No bluescreen or anything just straight to black.