PC shuts down after a second when turned on

Could be a bad motherboard, but try these steps and see how far you can get.

Strip it down and then add components back, one at a time, to try and isolate the offending component.

Turn the power off and unplug the power cord.

Disconnect everything externally connected except the mouse and keyboard (printers, USB devices). If you are not using a wired mouse and keyboard see if you can borrow one.

• Disconnect the power and data cables from all the drives inside the computer (Hard drives, DVD/CD drives).
• Remove all the cards installed in the PCI slots including the video card.
• Remove all the RAM sticks (same rules as above).

Now connect the power cord and turn the PC on.

• The motherboard should start beeping. You should get a beep code that tells you there is no memory. This is good, it means the processor is functioning and the motherboard is good so far.

• Now add one stick of memory in Slot A1 and power on. I guess your CPU has integrated graphics. Do you get more beeping at this point?

If you get no video then switch the one memory stick installed for another one and test.

Continue adding components one at a time.

If at any point the PC fails, the last component added was the problem one.

If you removed everything and there is only the motherboard (with integrated video), processor, and power supply to contend with and it does not POST or show anything on the screen, then the problem is one of those three.

If you have tested by using another power supply then you are down to two. CPUs rarely fail, so motherboard is the most likely guess.

Try to clear CMOS or replace the motherboard battery as a last ditch effort. Both long shots, but what do you have to lose at this point.