Reformatted my hp laptop and it messed up my external drive

I have two external WD drives that I used on my laptop. I was having trouble with the laptop so copied all my files to one external drive, reformatted my PC, and copied all my files back to laptop. Now, neither external drive can be accessed and it is asking if I want to format. Any ideas what I did wrong? I followed the instructions and used the 64 bit disk when redoing laptop. Could the laptop possibly have been previously formatted with 32 bit disk and this caused the problem?

Go to the PC makers website and make sure all of the drivers are up to date. There may be updated USB drivers there. Do the drives show in Disk Management? 

Joe