PowerMac G5 Wont Startup - Dead Battery???

Hey yall, I have a 1.6 GHz BASE model PCI G5 with 4gigs of ram (maxed) and 80 gig hdd. My concern is that I unplugged it for a schedued power outage, and now it wont boot back up. Worked fine before. I replaced the PSU just in case, but same thing happens. The light on the front stays on for a second, then shuts off. No internals can be heard turning on. It has a 3rd party power cord, but it has been working just fine - first one was getting worn. Any ideas? Could it be the "VRAM Battery"? Thanks