96 regal stereo

I recently left an interior light on and the battery went dead.
I boosted the battery and accidently left the key in the on position BUT the radio was off(there was still a little juice left but not enough to start)
I didn't notice anything when I boosted BUT now I have no stereo. I have checked the fuse and wiring and it all looks good.
the stereo has AM/FM cassette and CD and I think the anti-theft feature.
Is the anti-theft the case and if so how do I unlock?
I do not have an owners manual and the haynes book I have doesn't talk about it.

you will have to either call or visit the buick dealer there is a vehicle specific unlock code. any time power is removed from the radio it locks up, that way if someone steals it it is no good. i think it would have been in your owners manual but you don't have yours you said so the dealer is the only way......Sorry