@tano32 - Agustin, Sadly this one slid by us back when it was posted. I hope Dimitris got his system running again.
What likely happened is when the hair dryer was pulled out of the outlet still running it created a power surge which caused the iMac's power supply to fail. This is why we strongly recommend using a good surge suppressor to protect from such events. It could have been a lightning storm or other event along the power line that could do you in. In some places the power is very dirty! In fact here where I live in the city our lights constantly flicker (LED lights more so) as it's so bad. We use UPS's as surge suppressors wear out from it being so bad. And we have a building suppressor added as well to the buildings fuse panel.
So getting back to what the symptoms are telling us here is the diagnostic LED (LED#1 on) the power supply is damaged and needs to be replace. Here's the IFIXIT guide you'll need to follow: iMac Intel 21.5" EMC 2308 Power Supply Replacement.
For reference here's what the diagnostic LED's tell you: iMac Intel 24" EMC 2134 and 2211 Diagnostic LED's Apple still uses them in there iMac's so don't be concerned on the fact this is not the same model as your's. Jump to Step7 for the writeup on the LED's.