please install following D420 laptop computer driver in the ordered sequence. all drivers are provided by DELL.

DELL Notebook System Software driver
ftp://ftp.us.dell.com/utility/R171888.exe

Intel Mobile Chipset Driver
ftp://ftp.us.dell.com/chipset/R114079.EXE

Broadcom network Driver 57XX Gigabit Integrated Controller
ftp://ftp.us.dell.com/network/R116101.EXE

Intel(R) PRO/Wireless 3945ABG Network Connection driver
(R) Wireless WiFi Link 4965AGN
ftp://ftp.us.dell.com/network/Intel_multi-device_A13_R171131.exe

Wireless 360 Module with Bluetooth 2.0 + EDR driver
ftp://ftp.us.dell.com/network/Dell_Wireless-360-Module-wit_A01_R155172.exe

Intel 945GM Graphics Controller Driver
ftp://ftp.us.dell.com/video/R153830.EXE

Ricoh R5C843 Driver
ftp://ftp.us.dell.com/chipset/R141246.EXE

SIGMATEL STAC 92XX C-Major HD Audio Driver
ftp://ftp.us.dell.com/audio/R171789.exe

Conexant D110,HDA,MDC,v.92,modem Driver
ftp://ftp.us.dell.com/comm/R114200.EXE