Please help! Computer won't start, only beeps.

[SneakLerd]

I've had my computer for 5 years, it recently shut down before windows logon. I reinstalled it with win 8.1 and I was able to logon, but the moment I click download the computer shutdowns. I then thought the reason was the PSU, so I kind of swap the PSU, with one from my other computer. The only dumb thing is that I do not have 6-pins on my other PSU, so I had to use the original PSU togheter with the new one. The problem is now that the computer won't start at all. I press the button, and it has one long beep followed by three short ones. Which means the MB can't find VGA, according to Asus MB. I have swap around all the components and cleared CMOS. Nothing working. The MB has no integrated video output.I have also tried to use only one GPU, but does not work either.

Components:
PSU - 750w
MB - Asus p5n.d
GPU - 2x MSI
CPU - Intel 3.16Ghz
RAM - 4Gg/800Mhz

Edit:
I now removed the other PSU, the PC now starts, and runs. I got on a program called "Speccy", which has all of the temperatures of the computer. I can now see that the MOBO has an idle temperature of 100 degrees, and the CPU 80 degrees. Should I get a new MOBO, or can the PSU still be faulty?

 

[Zerk2012]

100C or 100F

 

[SneakLerd]

100C or 100F

Celsius

 

[BadAsAl]

That is hot for idle. What type of cooling are you using and are your fans running?

 

[SneakLerd]

That is hot for idle. What type of cooling are you using and are your fans running?

I use fans for cooling, the CPU has a stock fan. All my fans are running, at full speed.

 

[nuttynut]

100c on the mobo isn't hot; it's nuclear. Maybe it's actually the VRM temp? I've also never heard of Speccy, so I'm not sure that I would trust it.

 

[SneakLerd]

100c on the mobo isn't hot; it's nuclear. Maybe it's actually the VRM temp? I've also never heard of Speccy, so I'm not sure that I would trust it.

I have used Speccy for years, and I also use it for my other computer, it's trustworthy. There is one specific component of the Mobo which is superhot, I burnt myself the first time I wanted to check what was wrong.
The component is the one with "Asus" written on it.
http://

 

[nuttynut]

100c on the mobo isn't hot; it's nuclear. Maybe it's actually the VRM temp? I've also never heard of Speccy, so I'm not sure that I would trust it.

I have used Speccy for years, and I also use it for my other computer, it's trustworthy. There is one specific component of the Mobo which is superhot, I burnt myself the first time I wanted to check what was wrong.
The component is the one with "Asus" written on it.
http://

I'm going to assume that that's the Northbridge. It should get a little warm, but I've never heard of it getting superhot like you say.