Need to be more specific. Is it cranking? What have you checked for so far?
Check the basics, fuel, spark, and compression. I'd start with spark since you just had everything unhooked. You may have forgotten to plug something back in.
1995 Firehawk #528 resto-mod underway
Planned 383 rebuild: 195cc competition LT4 AFR heads, custom cam grind (still debating specs), 6" or 5.85" rods, forged internals
Upgraded T56: Viper mainshaft and 2nd gear, steel 3/4 shift fork, Billet keys 1-4, bronze shifter cup, internals Cryo'd and REM'd