Intel D850MV Mobo Not Powering Up (Standby Power Indicator LED blinking)

I have a fairly old tower with an Intel D850MV desktop mobo running a 1.7GHz
P4. All the RAM is seated properly, as are AGP and one PCI card. CPU
seated fine too. Checked the wires, everything. The system was working
fine up until yesterday when I turned it on, the Power LED lit up, but
nothing else. I pressed the power button to turn it off, waited, tried
again but got the same result. I let the system sit overnight and tried in
the morning. The Power LED doesn't light anymore, and nothing happens at
all. Opened up the case, cleared out all the dust bunnies, and I noticed
that the Standby Power Indicator LED (CR7F1) is blinking green. I'm not
sure if it's my power supply (hasn't been replaced since I built this
computer many years ago, at least 3 years). I can't find any
troubleshooting info about this LED blinking. Any ideas? Thanks in
advance.

Power Supply Specs:
Antec PP-303XP 300W (ATX12V)

--
Josh