computer wont even boot to BIOS menu

for the past few months, my computer doesn't want to boot. I tested my RAM, graphcs cards, blu-ray burner, and HD, the only thing I couldn't test were my psu, motherboard, and cpu. hopefully the problems lies somewhere in there. I did get a BSOD and looked at the dump and it pointed to my RAM, so I ran memtest overnight and it didnt find any problems so I'm wonder if my motherboard RAM slots are faulty? I also used a cooler masters psu calculator to see if my system was underpowered. I have 750w and it said I needed at min. of 786w, but it suggested the same psu that i was using. anyways, every once in awhile I can get my computer to boot if I remove and reinsert my hardware. Once my computer boots, I have no problems. The problem happens when I have to shutdown the computer. Once I shut it down, it wont boot. and suggestions?

wow im a retard. I didnt have my monitor connected to my video card. it booted with 1 video card, but that pretty much messed up all the tests I did cause my monitor was in the wrong port the whole time, but I'm not sure if thats the problem because last night i played a good 4 hours with both video cards and not a problem. then when I started my computer up this morning it wouldnt boot. is there anyway i cansee what wattage my psu is putting out?

ok, i did some researching and im well above my min. power supply requirement. I started up my computer with both video cards and it ran fine.

i believe so. correct me if I'm wrong.