I unplugged my 531S removed the top cover and used a small air compressor to blow out dust and dirt. I replaced cover, plugged it back in and now it won't turn on. Small green light is lit on back of power supply.
I'll suggest resetting your CMOS clock. With the computer unplugged from the wall, remove the small watch battery from the motherboard for about 10 seconds and then put it back in. Hopefully your computer will start up and tell you to set the system clock.