my macbook won't start-up, so i tried "safe mode" booting but the computer has been on for 8hrs

I'm Ubam, I have been using Macbook pro 500gb 5400-rpm hard drive, 4gb of 1333mhz DDR3 SDRAM, 2.4GHz dual core Intel core i5 processor; for 2yrs now.

The problem i'v encountered now is, I pressed the power button to shut down & it did, so now it won't start up, so I tried putting it on but everytime I press the power button it shows the screen light before login it then goes off, so I tried a "safe mode" by pressing the shift key, after that the Apple logo comes on & it has like that for 8hrs & I'm still waiting. Thanks