i always use an air compressor to blast out the crap, a vacuum is not going to get hunks of dust/filthy in areas you cant see,

so maybe you pushed a hunk of crap into the psu area and it shorted out…

or when you put the computer together there is a header that has pins that all line up, they can get bent over, cause a short,

also when you attached the SSD, maybe you some how crossed the power with the SATA to IDE adaptor.

i would start by blasting it out with a real air compressor and a blow gun.