Laptop won't start on the first try.

I've had an Acer aspire 5735z for around 4 months now. Everything had been working fine until a month back when I tried to turn the laptop on but it wouldn't power up on the first try. Now whenever I shut down the laptop I have to keep pressing the power on button again and again for it to start up, sometime's it starts up with a minute and sometimes it takes upto 10 minutes. The laptop works fine after it starts up. There's just the turning it on problem.
Please help me with this.