The R4 (100k) discharges C1 (100nF) when you press the button. When the Pin3 of IC1A reaches 0V, the Q (Pin5) goes to low level (0V) to turn the PSU on.
If your 100nF capacitor is defective, the circuit can reacts in a wrong way.
Also, note that you should keep the button pressed for some seconds (or some fraction) until the circuit reacts. This time is determined by the C1 and R4 values.
Try to reduce the R4 value to 47k and below, until you find a satisfatory timing.
I don't recomend to use a wire in the place of the R4.
