Most likely you lost or misaligned the connector between the slider and the mainboard...
See the small white plastic connector in
this picture
Best thing to do, unscrew the two screws underneath that side of the reader and remove the top strip and the plastic connector. Realign the connector underneath the slider and the mainboard, replace the top strip and put back screws.
Shoot take about 5 minutes to do this.
Gr.
William