I installed mp550, but now I got mp276. When I press the scan button in mp276, it does not pop up the scaning screen.
I cannot install mp276 Navigator, as when I install it, it pops up a message saying that a newer version has been installed.
Many MP Navigator versions are made for a specific product and so when you are installing a software from the same company which has a different version than the one supported by your product you'll face incompatibility between the device and the software. The software will not recognize your device because it has no memory of the settings or the way buttons work on the device. Using Add & Remove Programs found in the Control Panel, remove everything that it's related to the device and the software and then perform a new installation of the software SPECIFIC to your device.
Although the newer version of the software has been improved, it seems that it lacks or ceased support for the product you're having.