Is my power supply dead? My PC turned off randomly today and it won't turn back on!?

The light next to the power switch on the front of the CPU illuminates but the PC doesn't boot. I hear no sounds whatsoever from the internal fans, the disc drive won't open, nothing. I'm hoping it's just my power supply, but I really want to confirm it first before I go invest in a better one. I'd post the specs of my PC but since it was put together by someone a few years ago and sold to me I didn't think to keep a list on hand. I'm wondering also if perhaps I need a stronger power supply as I have installed a more powerful graphics card but I'm not certain of that either? Any help on this issue would be greatly appreciated. Thanks so much for your time.