Computer only boots up sometimes, power light on if it doesn't

[overview5]

Hello,
I would greatly appreciate help with my problem. My PC, an Acer Aspire AM5641-U5630A with Windows Vista, only starts up sometimes. When I press the power button, the blue power light comes on and the fans start sounding. However, after it quiets down there is no beeping noises and a display does not come on. On times in which the computer does turn on, a beeping noise is heard and an Acer logo display comes on before it proceeds to start up like normal. Once I'm past the Acer logo the computer works fine. It seems to be random as to when it powers up but I have tried an upwards of 20 restarts before.

Thanks,
overview5

 

[Tmagic650]

This is most likely caused by a weak or failing power supply. Open up the case and make sure that the fans are running and everything is free of heavy dust and other debris...

 

[overview5]

Thanks for responding. A bad PSU did cross my mind, however I wanted someone real tech savvy to confirm my thoughts. Is there any other reason which would cause this problem that I should know before I go out and buy a new PSU?

 

[Tmagic650]

I didn't think you wanted to replace the motherboard...