Computer doesn't detect printer on installation

Is it a usb printer? if so follow this:
Device Manager displays only non-Plug and Play devices, drivers, and printers when you click Show hidden devices on the View menu. Devices that you install that are not connected to the computer (such as a Universal Serial Bus [USB] device or "ghosted" devices) are not displayed in Device Manager, even when you click Show hidden devices.

1. Click Start, point to All Programs, point to Accessories, and then click Command Prompt.
2. At a command prompt, type the following command , and then press ENTER: set devmgr_show_nonpresent_devices=1
3. Type the following command a command prompt, and then press ENTER: start devmgmt.msc
4. Troubleshoot the devices and drivers in Device Manager.
   
   NOTE: Click Show hidden devices on the View menu in Device Managers before you can see devices that are not connected to the computer.
5. When you finish troubleshooting, close Device Manager.
6. Type exit at the command prompt.
   
   Note that when you close the command prompt window, Window clears the devmgr_show_nonpresent_devices=1 variable that you set in step 2 and prevents ghosted devices from being displayed when you click Show hidden devices.

1. Right-click My Computer.
2. Click Properties.
3. Click the Advanced tab.
4. Click the Environment Variables tab.
5. Set the variables in the System Variables box.