Reinstalling Steam is a more drastic measure but can sometimes fix deeper issues related to the Steam client's core files. Note: Your installed games will not be automatically deleted if you follow the correct procedure, but it's always wise to back up your game files if possible.
"The program can't start because steam-api64r.dll is missing from your computer. Try reinstalling the program to fix this problem." steam-api64r.dll missing mortal kombat x