[SOLVED] PC randomly shuts down?

Gigabyte ga-f2a88x-d3h
A10 cpu
4gx8 adata ddr3
550w psu solid gear

The cpu is liquid cooled.

So the issue we are having is when we had to reassemble the PC after it was taken apart and stored for a while is it will boot up, however it shuts right back down after posting into bios.
I honestly get 3 seconds to scroll through bios before it just shuts off. I have tried clearing the bios and different ram any other suggestions... Ps psu is brand new.
 
300w PSU will be fine if there's no dedicated graphics card installed, but make sure you buy a quality brand like Seasonic, Corsair or EVGA.
I generally due it's not my pc i honestly didnt do any research into the psu that was bought to replace the old one. I was just told this was and issue before the psu was replace thats why the pc was put into storage disassembled in it's boxing, so i told the owner to get a new psu and the problem continued but looking into it you are right cheap psu not likly to be stable. It does post to it's bios with a 300w psu from a dell inspiron no problem so we will try again with a actual psu not a $50 dollar brick