2000 Blazer Wont Start

ok so i just put a new dash (bezzel?) in my blazer, unhooked the 4wd button, rear wiper, and light controls, put it all back together, and it wont start, it start for a quick second and dies, i can hear the fuel pump, but dont have my pressure test with me, i had it running right before i worked on it? at the moment i have the battery unhooked to try to reset the computer... could anyone give me some ideas?? please

Blowed fuse
Anti theft triped?
What is the security light doing?

hey there, after re-setting the Computer, it still would do the same, run for a split second, and die, my volt meter wasent even rejestering (was far under 9) after numerous tries all of a sudden the volt meter started to move up (slowly), so i cranked it over again and finally it started, ive driven it all day, but still wont charge like it use to (its below zero and the volts are just under 14??) im not sure was the security light was doing at the time... but i was thinking that may be it. how would you go about starting it if the security was tripped? thanks much MT2500 starting to see i can count on your advise haha.

Check the battery voltage at battery and fuse boxes.
Watch that security light to see what it is doing.
If it starts and runs a few seconds and then quits.
There is a relearn on security system.
Also check the fuel pressure and for good spark to all plugs and all battery voltages and connections.
Good Luck