PC turns on, fan spins, but it doesn't finish turning on. I think it is a power supply issue.?

So the fan spins as it turns on, but it doesn't do that slight pause when the PC clikcs over and starts and the monitor shows the Gateway logo. Its like it just doesnt load up. I think it is a power supply doing dead. It has slowly done this and I just restarted it, almost like you do with a cold car. (excuse my mack of PC knowladge) Before I buy a new power supply, wanted any suggestions on if it might be something else.