Unfortunatly your system is not listed so it isn't compatible. That doesn't mean that Windows 7 won't work on the system but there usually are a number of drivers that may not be avaiable for the system. I suggest checking device manager, click on start, then right click computer, and choose device manager on the link to the left. Look for any devices that may not have drivers installed for them. You can check support.dell.com for possible replacements, there are no official Windows 7 drivers for the D420 but the Vista drivers can sometimes work as replacments.