No boot chime or cycling boot chimes

Hello,

i an running an early 2009 Mac Pro wi that just stopped booting. At first I got no boot chime at all, just maximum fans for a while and then shut off. I reset the SMC, and then I would hear a boot chime every 10 seconds or so, but still no boot. My last action before restarting was to install an update to the driver for my NVIDA graphics card, but I can't imagine a bad driver would cause my computer to fail to boot entirely. Any ideas?

Thanks.