Default gateway is not available

I'm on Windows 7 with adsl2. Can connect to net no problems at all.

But, occasionally while my computer is downloading at night, when i check my pc sometime in the morning i'm not connected. The network box in the taskbar has a red x and when i click on to check it says the following.

" the default gateway is not avaiable" Reset the local area connection adapter.

when i view the network setting i click on the x between my pc and the house and its then fixed. This is all okay but is there anyway of stoppping it happening or getting it to fix itself automatically. Router all appears okay and has worked on other windows version so suspect its windows 7!

Any help or pointers appreciated