There are heaps of possible causes for network problems, too many to list here.
Your first stop should be in Windows Update, Optional section, to check whether
any drivers are listed for your hardware.
Once Windows is fully patched, go over all the methods listed in the following
network trouble-shooting articles, and let us know the results :
The most useful methods are repeated in all the above three trouble-shooting articles,
so just look for ones you have not tried yet.
Before doing any modifications to your system, ensure your backups are in shape,
and create at least a system restore point.
You can also delete the wireless adapter in the Device Manager and reboot,
so Windows can choose its own driver.
See also the thread
Windows 8.1 Broadcom limited connectivity Lenovo
for a procedure for going back to an older version of the driver.
You might need to experiment with the drivers that are displayed in the list,
and reboot after each one.