Black screen on PC and won't boot but....

Ok about 3 days ago my pc kept freezing/locking up -mouse wouldnt work either- So i had to restart from the power button..it restarted fine went into windows and right after putting my pc password froze before getting to the desktop screen. Again restarted with the button because it was just stuck on that screen with non moving cursor. Restarted to the black screen to boot into safe mode/ with networking /or start win normal so i tried it in safe mode (reading after should have tried the SM w/networking) anyways i got into the diagnosis thing which scanned the memory, hard drive, and umm 2 other things i think ...and all 4 came back as passed so i was going to run the disk check thing and it got to 50% complete and froze again... again had to hit the button and when i did and it started to load the screen was black and it said bootmgr missing (i think thats how it was put def bootmngr) press cntrl/alt/del to restart .. which i did then my power button on pc came on and the little orange light under it didnt (usually does and blinks when its computing im guessing) but the monitor then said no signal and i could never get anything else to come up or load. So i went online of course n tried everything i read such as...

• popping out the cmos battery - tried to restart - nothing
• then resat everything connected to the power supply - tried to restart - nothing
• took all the hardware i could out and memory sticks - tried to restart - nothing
• tried just 1 memory stick at a time- tried to restart - nothing
• of course cleaned it out with air and prayer (and im not even religious) and tried to restart - nothing
• messed with the monitor cord to make sure it was tight tried to restart - nothing
• and swapped sata cables (got my cdrom to open again) buttt tried to restart - nothing
• i didnt have an extra monitor to try but i tried a little flatscreen which i connected via hdmi and same thing happened with that said no signal
• even re thermal pasted under the fan- tried to restart - nothing

Ooh also when i hit the power button all the fans (3 of em) were working .. i heard no strange clicking from hard drive (read that somewhere) .. i 've never in all the years ive had the comupter saw a green light on the motherboard nor heard beeping...at anytime even in past hardware updates =/

System specs
hp 6310y
win7
AMD Athlon II X4 630 / 2.8 GHz
ZOTAC GeForce GT 740
my bro replaced the power supply to suit the change in graphix card so im not sure of it
insignia is the brand altho that prob doesnt help much
and just incase the monitor is hp 2009m
and just reg mouse & keyboard

I think this is all of it.. sorry for the novel trying to do all i can before taking it to a repair shop that i really cant afford right now. Thanks in advance for reading & help .
oooh and most of the posts ive read people tell you to go into BI0S but thats impossible because the screen isnt coming on..unless theres a trick xD