Hi, n00b here, i'm a guy who destroyed his first (i.e. current) self-build computer (feel free to ignore, i probably would):
# 500W might be underpowered for the GPU you have. Also, you never stated your exact GPU. Thing is, you said you've been using it (presumably with the same listed spec) for 3 years, so it may be something more complex.
# You can check if your PSU is giving enough juice here: http://www.coolermaster.com/power-supply-calculator/
# Also, it has been said that the CX series isn't for heavy use. As for your CPU, i don't know a shred about AMDs, but maybe that's also eating up power. Did you overclock it at some point? Corsair CX has been said to be poor performing for overclocked systems, but great for factory settings that on the face of it can get by with 500W.
# TL;DR: Maybe your PSU isn't giving enough juice
or - maybe your PSU has just broken down because of the cheap capacitors used in the CX series
and / or - maybe you tried to OC at some point?