You probably need Dell drivers for the new OS. 

Windows 7 will install many drivers, but it will not install all of the required Dell drivers. Also, some functions that were available in Vista with the factory load may not be available in Windows 7.  Generally, the correct install is (1) Install Windows (2) Install Dell Laptop System Software (3) Install motherboard (Intel) chipset drivers and finally (4) Install device drivers including Video DELL Sound driver, ethernet, and whatever else is needed.   The motherboard chipset drivers are key to a successful install. 

HERE is the Dell downloads for Windows 7 64 bit for this model.