what would cause the power locks,radio/cd and trunk relase to stop working at the same time in a 99 buick park ave ultra. power seats went out a few months ago.

Most likely a fuse has blown in the power feed to the power locks, radio, and trunk release. The same may be the case for the power seats. If a replaced fuse blows immediately, you have a short somewhere. If the fuse holds but blows again later, one of the devices on that fuse is shorting and only draws excessive current when a specific function is used.

I’d look at the fuses. Maybe some have blown.