What make PC?
What type of (second) drive - SATA or EIDE; likewise type of orignal drive?
Do you know how to access bios settings (aka setup on many systems these days) at boot up time; and thus able to view bios settings?
Is the second drive found/listed in the bios settings?
If EIDE are you using Master/Slave jumper arrangement, or Cable-Select (CS) option?
If EIDE and Master/Slave option - are jumpers set correctly?
If EIDE and using cable select then is that the option on both drives - and is the Master at the end of the (single) ribbon (and the new drive in the middle)?
If EIDE then is the second drive installed a Slave to original Master; or is it on the second controller connection. If the latter then is it in Master or Slave position there?