Dell Studio 540 alive 1 min dead the next

Hello all i have a 3.5 year old Dell Studio 540 as described in the title and it wont power on At ALL. when i plug it in only thing that happens in the light on the back of the power supply comes one. when i press the power button NOTHING happens; no fans no lights no beeps nothing.

Everything is stock except:
a nvidea 8200gs GPU
and cavier black 1TB HDD

This what happened..

my computer was on as it usually is (i pretty much leave it on always). i sprayed it down with canned air while it was on. then shut it down removed all the wires (pulled power cable from back of PSU) and sprayed it down again. i plugged another computer that i'm working on in it's place (plugged power cable to back of PSU) connect mouse and keyboard. i powered it down 1 more time and replace my Studio. i plugged the power cable then the mouse and keyboard and hit the power button. it booted up fine and got some files of and unplugged everything again. basically repeating what i did with the other computer. i went to hook my Studio up the second time as i did the first time; plugged the power cable into the PSU and hit power button. NOTHING happened, so i'm a bit disturbed as to what happened in the 2 mins i had it disconnected.

i didn't touch any components on the inside. all i did was spray it down with canned air a few times. i dont notice any weird smell that i can recognize. i do see a weird residue on an inductor i can see through the back of the PSU fan. obviously i'm praying its the PSU but i'm also optimistic that the power button has just malfunctioned.

I'm going to strip the computer down and check everything wire connection and every component and see if i can find anything. i have read lots of info about this PC just dying, but it was more of a come to turn it on 1 day and its dead not i'ma alive now i'm dead kinda thing.

any suggestion of any kinda wold be greatly appreciated