Apple //c Problems

["Dave A." <dwaynedibley@yahoo.com>]

I'm just getting back into using an Apple // after many years of PC 'fun'.
Have managed to get my hands on a //c with External Disk Drive but every
time I switch it on,  it gives me the error message "Check Disk Drive".  I
have to admit that the lessons learnt in all my years of Apple tinkering
have deserted me and I cannot remember what this indicated......Have tried
all sorts of program disks, etc. to no avail.

Any help/comments gratefully received!