I have a Sony Vaio RB40 and the cpu overheated. I turned it off and waited overnight to turn it on. When I plug in the power cord the light on the psu and the mobo blinks and the pc will not power up. If I unplug the 24 pin cable from the mobo then plug in the power cord to the psu the light on the psu stays solid. Do I have a bad mobo? Thanks for any help!

Hmm, to test the mobo take out the Ram DIMMS.

You should hear a pattern of beeps.

When you turn it on do you or did you hear a Siren?

If you don't hear the pattern then there is a fault with your motherboard or Processor.

P.S. it would be wise to remove everything. Pci CArds, USB devices, Leave only the Bare Minimum.

CPU w/heatsink and PSU. (No Ram no Graphics card unless it's built in).
This is to test whether your mobo works.

If you hear the Beep Pattern. Turn of your PC.

After you have established the Beep Pattern Exists. Re-insert your Ram.

You have to fix the issue of overheating. Unmount your Heatsink and readjust it it should be very secure. you should be able to lift your motherboard with the heatsink without any wobble. (Ofcourse don't try this if the motherboard is secured to the case)

Now add your graphics card and test if you get the screen.

Now add your components one by one and booting to see if it worked. This is to test if all your components work.

Tell me how it went.

I unplugged everything from the mobo except for the cpu. It is doing the same thing it did before. As soon as I plug the psu into the mobo and insert the power cord I get a steady blinking green light on the psu and mobo. It will not power up, only green lights blinking. I assume if it is the cpu or the mobo I could probably just buy a cheap new tower for around the same price....

So no beeps huh. Yeah then, It could be processor or the motherboard.

You seem to know your options, please mark as solved if solved.

Yeah, no beeps or siren. All I get is the blinking lights. Thanks for your help!