from each step. My guess and that is all it is, you have a short from motherboard to case or a bad motherboard at this point. Your are now eating up replacement parts, is this computer worth it?
Replacing the power supply would be about all I would and from your post you have done that. Next step, get a second opinion.
Try taking it to a repair place and pay the bench fee and let them tell what is wrong. You may save your replacement parts for your next build or repair. The last time I did this I paid 30 US dollars and was told the motherboard was bad. I saved buying and installing a lot of parts and time. It is your call. Good luck.
A few days ago my computer started randomly locking up over night. I'd just restart and it would come up fine. Then one morning I go to access a sata drive that I used for storage and my computer locked up. I restarted it, went back into the drive same thing. I figure maybe there was something wrong with the drive or connection so I unplugged it. My pc started fine. I went to work and came home to my computer no longer booting all the way. It would go to the windows boot screen and and just restart. After swapping that IDE drive into another pc as a second drive windows detected many bad sectors. I realize this drive is done for and then tried putting the sata drive in to see about getting my data off of it. It would spin up but the pc would never recognize the drive as there. This one is probably dead as well. I then Dismantle my whole pc to try and look for any noticable problems. I noticed some black on the power supply and took it appart and found some damaged compontents so i threw it away. I then examined the motherboard and saw no noticable issues with it. I put it back in its case and hooked it up to another powersupply and put just a video card in it, it loaded fine so I hooked up another IDE drive and it recognized the drive fine. I partitioned the drive and then went to go install windows. It then seemed to be having trouble reading the disk in the cd drive and I went to power it off the button was not working. I went to pull the power cord out and plug it back in and as I was just pushing it in, I noticed a smell and heard some crackling coming from the back of the power supply. I haven't turned it back on since. I think this power supply is now spent as well. I'm just not sure why. Any ideas would be much apreciated. thanks!