Computer not starting when...

oh yeah forgot to mention the problem, i ordered a new case and the PSU slot is at the bottom, and the cord for the cpu fan is too short

in my old case it was at the top so it was long enough
 

The CPU fan MUST be plugged into the CPU_FAN header on the motherboard (not directly to the PSU).
 



not sure if you got my point but let me clear my answer

there are 2 x 4 pin sockets near my cpu fan

1st is the CPU fan which is plugged

2nd is for PSU ( pc wont start if its unplugged )

i have no idea why does it even need the psu one, the fan spins without it, but pc wont start...

 

I think you are referring to the 8-pins CPU power connector located near the CPU socket.

Yes now I understand the situation. The bottom mounted PSU does not have a cable long enough to supply power to the 8-pins connector. You can use a 12-inch extension. I will look for one at Newegg.