Is network card disable when u are working? Sometimes it will be issue related to virus, Or Update ur network card driver or re-install drivers,
Now run regedit and navigate to the following key >>
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services
Do a "Find" for the driver name for your card.
In the right pane where this is found you will see a "start" type -- this is "manual" by default (at least it is for mine).
Try either setting it to "automatic", or "boot".
Change Value data to the wanted state:
0 = Boot
1 = System
2 = Automatic
3 = Manual
4 = Disabled