Laptop won't connect to network after reboot

I have a Dell Studio laptop(Windows7) connected to my network thru a router and an ethernet cable--When the laptop is rebooted the connection is lost even though the other 2 desktop computers are still active--same thing when I use a wireless router when I'm in another office--This just started in March--the solutuon is that I have to reboot both the modem and the router and then all is OK but if I reboot my laptop or it is automatically rebooted after any updates--same thing happens----I have checked and updated all the drivers--I am certain the router is fine as both of my other computers have never lost their connection--only this laptop----any suggestions???