I have a 96 Blazer with little over 100,000 miles on it and it won;t do anything. On Monday got in turned key and fuel pump came on etc. then when i went to turn key to engage starter-it totally blacked out-just like the battery was totally dead. Had a girl help me jump it and as soon as we hooked the cables up and i turned the key it started instantly. Later that evening was coming home from work and the headlights,dash lights started dimming out and the rpm gauge almost went to 500 rpm but only lasted a second and came back up and all was fine. Things fine for days then leaving store and get to stop sign and rpm drops, emergency brake light comes on and tone goes off for couple seconds then everything ok. Get home go to start again and nothing like battery is totally dead. Waited couple hours and started up fine. Next night it started up put in drive went about 20 feet and it totally blacked out and has been that way since. I have checked battery cables, plug connections, checked battery voltage (12.8) and checked fuses in fuse panel. But it will not do anything--no gauges,no lights, no nothing. What is going on???? Please help if u can.

Check the fusable links under the hood over the driver's side wheel well. There are also links in the wires going to the battery. Most of these links supply constant power to the ignition/starter circuits.