Normal cycle on control panel is frozen. Other buttons work.
What part do I need to replace?
Here your parts
http://www.appliancepartspros.com/partsearch/modelsearch.aspx?model=PLD2850RDC0
Not sure what you mean by frozen.
Frigidaire does not publish the pin outs for the keypad so try the following cleaning/check.
If that does nothing then I would probably change out the keypad first.
Unfortunately it is a crap shoot.
Connector Cleaning / Checking
Unplug the unit
Open it up
Remove the ribbon cable from the keypad to the control board at the control board.
Clean the edge connector.
If it is the type where there is not a connector just the insulation is removed, it can be cleaned with a pencil eraser. Do not use an ink eraser as it is too abrasive.
Check the tracks in the ribbon cable for hairline cracks. A magnifying glass helps here.
Would not hurt to clean the connector on the board. Use electronics contact cleaner or isopropyl alcohol and a tooth brush. Be gentle and do not reconnect till all the solvent evaporates.
Reconnect everything and give it a try.