PC Struggles to power up when cold – left off for a few hours

Hi, please help. When pressing the on button on my pc first thing in the morning it ticks over rapidly, i can hear a fan turning, the green lights on the keyboard and front of the pc blink rapidly but the pc will fail to turn on. It will finally power up after holding the power button whilst flicking the power supply swich at the back – after several attempts. Once the pc has been on for a while it will switch off and on okay. This morning used a hair dryer to try and warm the pc up, and it started after afew attempts – this is not very practical though!