computer won't start

[trscc84]

I have a 2000 Powermac g4 733mhz 40 gig, 512 mb memory

Last week my computer would start, but it would get stuck on the blue bar load screen, I called apple, and they told me to press and hold shift to put it into safe mode. Before i could even do that, it decides to not turn on. So is there anyway to turn it on?

Thanks