Have you put a new copy of windows on pc since you got it?
C drive is a partition, its a area of your disk assigned the title C. On laptops (and some pc) there can be a hidden Partition set aside to hold a copy of windows that would be used if you choose factory reset - it also includes all the drivers that were available at time pc was made.
If you have put windows 7 on since you got the pc, its possible you deleted the recovery partition and that is why you are getting this error now
try here and see if you can get a recovery dvd: https://serviceshop.asus.com/