Somehow the new drive may have been set as the first boot device.
First you need to enter the BIOS. This normally means pressing a key, or combination of keys, immediately after switch-on. A message to this effect usually flashes up on the screen when you switch on, such as "To enter setup press Del". Other common BIOS codes are listed at click here.
When the BIOS screen appears you will see a set of menu options. Look for one labelled Boot or Startup and select the item Boot Order, or First Boot.
Change the setting to read the serial number of your hard drive drive (or HD0 or HD1, depending on your BIOS), Save the Change and Exit the BIOS. Restart your computer.