Please follow these steps:
1. Press wrench and screwdriver button on your PIXMA MX870.
2. Use the arrow keys to select Device Settings and press OK.
3. Use the arrow keys to select LAN Settings and press OK.
4. Use the arrow keys to select Confirm LAN Settings and press OK.
5. Select Print LAN details and press OK.
A page will print.
4 lines from the top is SSID. Please make sure that the name listed there is the wireless network name that your computer is connected to.
6 lines below that is Signal Strength. That number should be above 75%. It is it 30% or lower, please move the printer and/or router closer to each other.
2 lines below that is the IP address. Please take note of this address.
On your computer, please press the Windows key on your keyboard and the letter R, then let both go.
In the Run window that appears, please type CMD and click OK.
In the Command Prompt window that appears, please type:
PING and then the IP address that you noted above. For example, if the IP address was 192.168.0.24, in the Command Prompt window, type:
and then press the Enter key on your keyboard
In the results, go you get request timed out? Destination host unreachable? or at the bottom do you see "Sent = 4, Received = 4, Lost = 0"?
If you get request timed out, that would indicate that your PIXMA MX870 is not connected to the same network as your computer. Please either connect your computer to the same network as your printer or connect the printer to the computer's network.
If you get destination host unreachable, turn your printer off. Disconnect the power cord to your router for 15 seconds and then reconnect it. Once the router is back online, turn your PIXMA MX870 back on. Your computer should now detect your printer.