1993 Chevy Astro No Start

I turned off my vehicle at about 12:05 am, woke up and tried to turn vehicle on at 4:30 am and clicked for 1 second and died. I checked voltage at battery and read at 12.88- 12.90v w/ a Snap-On DVOM. Vehicle has no working lights, will not start, instrument lights will not come on. Absolutetly nothing comes on when turning on key. Recently had a aftermarket stereo system installed along with amplifier and subwoofers done by myself for about a month now but had no problem whatsoever. Did not have this problem before. I was told to check Fusible Links but not sure where they are located on my 1993 Chevy Astro. Please help???